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A Detailed Discussion
about Water Filtration

Owners of pools and spas of every shape and size — residential pools, commercial pools, health club spas, whatever — are driven by a singular desire for clean, clear water. For that reason, every service technician must have a working knowledge of filters. The filter is so named because its job is to remove suspended particles from the water — an essential factor in reducing turbidity and enhancing water clarity. Filters are universal in pool systems. linked to the circulation system along with the motors and pumps.

The motor converts electrical energy into mechanical energy used by the pump to circulate the water through the filter — which does its part by straining unwanted material from the water before it is returned to the pool. Although the principles of filtration are straightforward, the topic of filters is not uncomplicated, partly because several equipment options have come into use in the pool and spa industry. In the glossary that follows, we begin our discussion of the three basic types of filters — sand, diatomaceous earth and cartridge —by providing definitions for many of the terms you’ll encounter as we present a series of filter articles in up-coming issues.

Anode: A component, usually made of zinc or magnesium, that prevents electrolysis or galvanic action in steel filters.

Backwash: The process of cleaning the filter medium and elements by reversing the flow of water through the filter — and thereby flushing accumulated debris out of the filter.

Bridging: A phenomenon in DE filters in which the filter medium builds up between filter elements, limiting flow.

Cartridge filter: A filter that uses replaceable paper or fabric-like cartridges as the filtration medium.

Diatomaceous earth (DE): A powder made of fossilized skeletons of tiny plankton, called diatoms, that serves as a filtration medium when it forms a cake on the filter element.

DE filter: A filter that uses diatomaceous earth as the filtration medium.

Effluent line: The plumbing line leading from the filter equipment to the pool or spa.

Filter area: The filtering surface area through which water flows In the filter housing; measured in square feet,

Filter cycle: The operating time between cleaning and backwash routines.

Filter medium: The material used to filter debris from the water — usually sand, a cartridge or diatomaceous earth (DE).

Filter rate: The number of U.S. gallons of water that flow through one square foot of effective filter medium per minute during the operation of the circulation system.

Filter sizing: The process by which an appropriate filter is selected for a given application as determined by the desired flow and filter rates — and as governed by local ordinances.

Flocculants: A chemical substance (such as alum, for example) that promotes the combination or coagulation of fine suspended particles to assist in the filtering process.

Flow meter A gauge that measures the flow rate in gallons per minute.

Flow rate: The volume of water flowing past a given point during a specific period of time: measured in gallons per minute (gpm) or gallons per hour (gpm).

Grid: The rigid structures that hold and support flexible septums (or septa) in the filter housing.

Influent line: The plumbing line that leads from the pool or spa to the filter equipment. Also known as the suction line.

Multi-port valve: A valve that permits the multi-directional control of the flow of water through a filter; it combines the function of two or more single valves.

Pressure differential: The difference in pressure between the influent and effluent lines of a filter

Pressure filter: The most common type of filter: the water is forced through the filter by a pump mounted on the influent side of the filter.

Pressure gauge: An instrument that measures the water pressure in influent and effluent lines. An increase or decrease in water pressure indicates either cleaning or backwashing operations or a plugged line.

Sand filter: A filter that uses graded layers of sand as the filtration medium.

Septum: The part of the filter element or grid on which the filter medium, usually DE is deposited or caked,

Turnover rate: The time required to circulate a volume of water equal to the capacity of a given pool or spa.

Vacuum filter: A filter through which water is pulled by a pump positioned on the effluent side of the filter. Most vacuum filters use DE as the medium.

An effective filtration system is critical to the well-being of every pool and spa — no exceptions. Without proper filtration, maintaining water balance is impossible, and algae and bacteria will run amok.

The first step in building a good filtration system is selecting the correct filter for the job. The filter fits into the equipment sequence after the pump — so whether you're replacing an old filter or installing a filter on a newly built pool, you’ll need to match the filter to the pump and the size of the pool.

Let’s get started. Remember, the goal is to properly size and select the filter for a pool or spa. To do that, you must first calculate the pool’s volume and capacity. Next, you’ll need to compute the pool/spa flow rate and the filter flow rate. Once you’ve done all that, and have taken some other factors into account, you’ll be ready to select the right filter for the system in question.

The first step in finding the correct filter model is to figure out how much water has to be filtered. Here are some simple formulas and techniques to use when calculating the volume of a swimming pool. For a rectangular pool, multiply the length by the width by the average depth.· For a circular poo1, multiply the radius by the radius by 3.14 (pi) by the average depth. It is important to note that many oval pools are actually rectangles with semicircles on the ends. These are not true ovals and require either combining the formulas for circular and rectangular pools, or using the following technique:· For an irregular shaped pool —one that does not exactly fit the definition of rectangle, circle or true oval— it is easiest to calculate the volume by using a grid.

Make a scale drawing of the pool on a piece of square-grid graph paper, with each square representing one square foot. (Actually, you can make the drawing to any scale you want — so long as you keep it uniform.) Then simply count up the number of squares (don’t forget to estimate how many complete squares all of the partially filled squares would combine to form), and that will give you a close estimate of the pool’s area in square feet. Multiply the area by the approximate average depth of the pool — and there you have it. the volume in cubic feet,

Next you’ll compute the capacity —the number of gallons of water that the pool will hold (as opposed to volume, which is a spatial measure-ment). To calculate the capacity, simply multiply the pool volume by 7.48 (the number of gallons of water contained in a cubic foot of volume).

As an example, suppose you have a rectangular pool that is 40 feet long and 20 feet wide, with an average depth of 5 feet. Plug these numbers into the volume equation and multiply: 40 x 20 x 5 4,000 cubic feet. Now plug the volume into the capacity equation and multiply: 4,000 x 7.48 = 29.920 gallons. Simple, right?

The flow rate is the volume of water flowing past a given point during a specific period of time, measured in gallons per minute (gpm) or gallons per hour (gpm). To compute the flow rate, divide the capacity of the pool  by the turnover rate, which is the time required to circulate a body of water equal to the capacity of the pool. Let's say you want to set up the pool to have an eight-hour turnover rate. Your success in achieving that will depend to a large extent on which filter you eventually install, Therefore, you must first determine the desired flow rate — one that will facilitate the turnover you’re seeking. The equation to find the flow rate for the 29,920-gallon pool noted above (no matter what its shape) is: 29,920 ±8 = 3,740 gpm. To calculate the flow rate per minute divide the flow rate per hour by 60. In his case, 3,740 + 60 = 623. That is the rate at which you want the filter to work.

Stating this situation another way, the calculations for your 29,920-gallon pool show that you require a flow rate of 62.3 gpm to filter the pools capacity in eight hours. Therefore, your goal is to determine which model of filter will filter 62.3 gallons of water per minute—resulting in a complete turnover every eight hours in the pool in question.

To achieve that goal. you have to find a filter whose filter flow rate matches the desired flow rate for the pool. The filter flow rate is defined as the amount of water filtered over a given period of time — expressed in gallons per minute. To determine the filter flow rate, multiply the filter area by the filter rate. The filter area is the filtering surface area through which water flows in the filter housing— measured in square feet. The filter rate is the number of U.S. gallons of water that flows through one square foot of effective filter medium per minute during the operation of the circulation system.

If you didn’t follow that, don’t worry — all you have to do is get both figures from the filter manufacturers, In our example, let’s say you have a filter area of 5 square feet and a filter rate of 12.5 gpm. (These numbers are based on a popular model of sand filter.) If you multiply 5 x 12.5 you have a Jilter flow rate of 62.5 gpm —pretty darn close to our desired flow rate of 62.3!

Now you’ll need to consult filter manufacturers to find a model with the necessary filter area and filter rate. Once these numbers are provided by respective manufacturers for various models. you can calculate the filter flow rate to see which particular filter will match the need.

What type of filter do you prefer: sand, diatomaceous earth or cartridge? Pressure or vacuum filters? From your poolside experience, you probably already have a good idea of the type you like. You may even have narrowed it down to a preferred manufacturer— which will make it even easier to perform your calculations and select a filter that will do the job. The example we’ve used here refers to characteristics of a sand filter, It is important to note that both DE and cartridge filters have notably lower filter rates, Nevertheless, the mathematical relationships between filter area, filter rate and filter flow rate will remain the same. Never hesitate to contact manufacturers or their dealers to ask their professional advice in this area. For that matter, give your fellow service technician a phone call and get some input from another poolside pro.

When selecting the right-sized filter, it is important to keep in mind that as the filter removes debris from the water, the filter medium will become more and more clogged, and the filter will require an ever greater flow to clean an equal amount of water. It is necessary, therefore, to select a filter that is larger than indicated by our calculations of flow requirements. This is especially true for pools that get heavy use (commercial pools. for example) and for backwashing (because the filter requires additional size for backwashing). Using our example, you could either select a model with a larger filter area or a model with an increased filter rate To allow for debris buildup and back washing, you might select a model with a filter area of 5 square feet and a filter, rate of 20 gpm. That gives us a filter flow rate of 100 gpm — well beyond our desired rate of 62.3 Alternatively you could choose a filter with 4 square feet of filter area and a filter rate of 25 gpm per square foot,

In many cities and counties throughout the country, filter rates on pools are regulated. The National Sanitation Foundation sets maximum filter rates in order to ensure effective filtration since the faster the water passes through the medium, the less effectively it is cleaned. Filter-rate ceilings are imposed most often for commercial facilities. If this is the case where you live, you may have to compensate by selecting a model with a larger filter area, By doing so, you can achieve the same flow rate without exceeding the maximum filter rate. 

Taking all the above calculations and factors into consideration, you're now ready to select the proper filter for a particular pool.

A level start for clean water
Installing a pool filter is a fairly straight forward process. but it always requires care and the faithful following of a few basic rules The text below covers those basics. but before you start cutting PVC and lubricating 0-rings, remember that this is a generic guide and that you should always consult manufacturers literature before working with any unfamiliar products. Beyond that, once you survey the situation by inspecting the equipment pad, the plumbing design and the electrical system, you should be ready to go.

Sizing up the task at hand: When it comes to filters, some of the most fundamental considerations can make the biggest differences. Where the unit is located, how neatly it is incorporated into the overall circulation system and how it’s tied into the pool’s electrical circuitry are all very important.

Equipment pad: The equipment pad should be a flat, level slab of poured concrete, brick or concrete block. (Never install a new filter on wood, because it can warp or decay beneath the filter’s footings and compromise the position of the unit.) Three things to watch: First, filters should always be installed on a level surface; if things aren’t square. the unit may vibrate or operate to less than its optimum ability. Second, filters should be located as close to the pool as possible. Third, the filter should have adequate drainage and —in the best of all worlds — should be positioned to provide plenty of room for service access and maintenance.

Plumbing: The plumbing should be designed and installed with the shortest lines and the least number of fittings needed to achieve optimum water flow efficiency in the circulation system. If the filter is most conveniently installed away from the pool, however, increasing the pipe size between the filter and the pool will decrease the head resistance and compensate for a longer run. Inspect the plumbing so you can be prepared with the proper fittings and materials when you arrive. In addition to being bothersome, extra trips to the distributor to pick up unanticipated supplies can drive your job costs way up.

Electrical hookup: Although the filter is not directly connected to electrical power, the pump motor runs on electricity, which means that the filter must be grounded and bonded by a professional electrician. In addition, the electrical wiring and hookup of the motor must have been completed by a professional electrician in accordance with local and national electric codes,

Now that the pad is ready for the new filter, it is especially important to refer to the filter manufacturer’s installation manual for specific instructions regarding the particular make and model of the filter you’re installing. As was mentioned at the outset, the basics don’t vary much from brand to brand or even type to type; just the same, there are distinctions with each unit that must be considered

Once you’ve finished your reading, the first step in the installation is to place the filter on the pad. You might consider bolting the unit to the pad. although relatively few filters are mounted in this fashion. Next, connect the circulation plumbing to the filter. Every filter has two basic plumbing connections— the influent and the effluent lines. The influent line supplies water to the filter; the effluent line provides an outlet for water after it passes through the filter

A gate valve should be installed on both the influent and effluent lines. This will permit you to close the lines when it is necessary to service, remove or replace the filter. The plumbing lines are connected directly to the filter’s multi-port valve (some models have a push-pull valve) either by hand tightened union connections or, if appropriate, by bonding with an adhesive, such as a PVC cement. For threaded pipe connections, the application of PTFE tape to the threads before connecting the pipes is often recommended.

Be sure the 0-rings on all valve fittings are clean and that each 0-ring and 0-ring groove is lubricated with silicone lubricant. Install 0-rings in their grooves and tighten with the appropriate union collar. Before applying any adhesive, be sure all connecting points are clean and dry — and use the recommended primer before doping PVC components. Allow an appropriate drying period before pressure testing or operating the equipment — and take into account the fact that temperature and humidity may affect the drying time of some adhesives.

Once the filter is installed on the pad, all of the plumbing connections are set and the unit is properly grounded, it is time to put the circulation system into full operation. The three main types of filter sand, DE and cartridge — require different start-up procedures. As above, the following are general guidelines for your reference; manufacturers manuals will give you the specific help you need.

Sand filters: Most sand filters in use today are high-rate models in which water typically passes through a number of layers of sand and gravel that have been carefully placed in the filter tank. The size of the sand particles used as the filter medium is very important for optimum efficiency. If the sand granules are too big, filtering efficiency is decreased; if the sand particles are too small. the filter will clog up quickly.

Check the specifications provided by the filter manufacturer, then fill the tank with layers of coarse, medium, and fine gravel followed by the silica sand layer on top as directed. The silica sand commonly used as the top layer has a diameter between (0.35 and 0.45 millimeters with a typical uniformity coefficient of 1.4. Also, plan to leave a space between the sand bed and the over drain.: This space is known as freeboard, and most manufacturers suggest it should amount to half the depth of the filter bed. While most sand filters use several layers of material to clean the water, some models use only one or two filtering layers. Again, watch those manufacturer specs!

Flocculants are often used to improve the performance of sand filters. Most filter "flocs’ are alum-based preparations that form a gelatinous layer on the top of the sand. As an alternative. diatomaceous earth can be used: Add one-half cup of DE for each three square feet of filter area after the unit has been filled with sand.

DE filters: These units filter water by passing it through a layer of diatomaceous earth that coats grids inside the filter tank. The DE is added as a precoat to the grids, attaching itself on the grid-covering mesh known as the septa. Common practice calls for adding two ounces of DE per square foot of filter area with a typical variation of a half-cup either way depending on manufacturer specifications.

The DE should be mixed with water and fed into the filter as a ‘slurry," or suspended mixture. After turning on the circulation system, add the slurry via the skimmer at as steady a rate as possible to permit even coating of the filter septa. Ideally, the DE will form a uniform "cake" between 1/16 and 1/8 of an inch thick. DE can also be introduced to the filter by using a precoat pot. solution feeder or erosion feeder that is specifically designed for precoating.

cartridge filter: Setup of cartridge filters is simple: Insert the filter cartridge per instructions and fire up the circulation system. You can also use a flocculating agent for cartridge filters. With all types of filters, open the unit’s air release valve and turn on the pump. When a steady stream of water shoots out, close the valve. The system’s now hard at work! Manufacturers urge technicians and homeowners always to remember to open the air release valve when starting the filter, because air pressure in a filter can be very dangerous.

Safety first
Although were covering it last here, safety should be a primary consideration in filter replacement and repair — particularly with units outfitted with pressure-clamp assemblies, which, under certain conditions, can fly apart with tremendous force.. In fact, flying parts from a ‘blown" filter are often the source of severe property damage and, unfortunately, the cause of severe, sometimes fatal, injuries. According to experienced service techs, one of the key steps in avoiding such mayhem is getting the clamp assembly and 0-ring seated properly on the tank before pressure testing or starting the circulation system. Filter manufacturers often recommend tightening the clamp to specs using a torque wrench. Extra care in placing the assembly around the tank and tightening is critical, they say, with some recommending partial tightening of the clamp and then tapping the assembly into place around the perimeter of the tank.

Improper application of the clamp assembly may result in a poor seal that could cause the filter to blow. Alternatively, the uneven seal might slowly force the tank out of round over time and create serious problems in future servicing — and further increase the chance of blowout. A final safety tip: Whenever any repairs are done on a filter or related components, cut off all the pool’s electrical circuits at the source!

When a filtration system goes awry, the quality of the water can deteriorate quickly — and waves of service nightmares may soon follow.

If the troubles were limited only to algae gaining a foothold or to water getting murky, that would be one thing. But the fact is that poor filtration leads as well to increased chlorine demand and chemical costs, to a tougher water-balancing act and, eventually, to a real health hazard to bathers. The following outlines basic filter ills, defines probable causes and suggests solutions. For the most part, these dimensions cut across all filter types— diatomaceous earth, sand and cartridge. As applicable, however, concerns specific to different media are noted.

Please note that. these guidelines are for general information only; you should always consult manufacturer literature for specific recommendations and operating guidelines for each filter model you encounter in the field.

Before you read on. also tote this general rule: When checking an operating filter’s performance, tap the face or casing of the pressure gauge firmly to make sure the needle is not sticking. A gauge that fails to indicate a rise in pressure not only compromises your ability to monitor filter cycles, it can also be quite dangerous: Excessive pressure call result in cracking of the filter body or failure of the clamping device on the filter tank. Keep in mind as well that many symptoms of a malfunctioning filter system can be brought on by inadequate running time. The first step in troubleshooting is to simply make sure the system is running enough to stay on top of filtering demand.

Symptom: Reduced flow of water through the filter.

 As dirt accumulates on the filter media, water flow is restricted—and pressure within the tank rises. When the pressure rises to a level specified by the manufacturer, it’s usually time for routine backwashing of a sand or DE filter, or simple cleaning of cartridge filter elements. The ranges of operating pressures for filters vary widely, depending on type. A typical range for high-rate sand filters, for example, may be 10 to 15 pounds per square inch at the beginning of the filter cycle (that is, the period between routine back-washings or cleanings) on up to 25 to 30 psi when backwashing is required.

Conveniently, some filter systems mainly large high-rate sand or diatomaceous earth filters on large commercial installations — have pressure gauges installed on both the influent and effluent lines. As the media becomes clogged with dirt, the influent pressure will become higher than the effluent reading. When the differential between readings reaches a specified level, it is time for backwashing. Gradual pressure rises are normal in the course of the filter cycle; if the rise in pressure is relatively consistent, then normal backwashing or cleaning routines will suffice. If pressure begins to rise more rapidly than normal, however, it is time to take a close look at the elements of the filtration system.

Symptom: Short cycle between backwashes. Most often, short filter cycles indicate excessive flow rate through the filter. This indicates in turn that the filter may be undersized or that the pump may be too powerful for the system. If you are comfortable with filter-sizing equations, it cant hurt to do a quick check of the numbers to be sure equipment sized correctly. Your local filter dealer can almost always help you run the numbers if you get stalled on the calculations. Once  that’s all straight, install a properly sized system.

In other cases, short filter cycles indicate an unusual increase in the burden on the filter media caused by excessive dirt, debris, body oil, lotions, hair or algae. Very high bather loads (or invasions by pets or careless fertilizing of plants and lawns) lead to overworked filters. About all you can do here is discuss your observations with the pool owner to see if changes in routines are necessary (this could affect your billing); beyond that, backwash the filter as needed.

With sand filters and DE filters to a lesser extent — you can get into trouble when soda ash or coagulants are fed into the skimmer too fast, In these circumstances, the chemicals do not have sufficient opportunity to dissolve and, instead of passing through the bed in solution, clog the media and raise the pressure. The way to go here is to introduce these agents more slowly —or dissolve them before introducing them to the skimmer. Note: Alum should never be used with a DE filter: It will only solidify the filter cake. In addition, clogging of the septa in a DE filter — whether by rust, calcium build-up or soda ash— may increase the pressure and compromise effective filtration. If you suspect this problem, clean the filter elements and check for clogging of the tine nylon mesh covering the septa. Treating the septa to a light acid wash and hosing with a strong stream of water will usually relieve the problem.

Symptom: Inadequate filtering action. All of the troubleshooting tips in this category refer to specific filter types. In a sand filter if the media has been charged improperly or in inadequate quantities, channels may have formed in the sand and gravel bed, and may be allowing water to pass through unfiltered. Look for evidence of channeling or tunneling —and recharge the filter if necessary.· Also in a sand filter, if the unit has not been backwashed consistently, mud balls may have formed on the surface of the sand bed, thereby limiting filtering action. Or. in extreme cases, the sand may have calcified and will no longer filter out dirt. Look for mud balls or evidence of calcification; backwash or remove the old sand and recharge the filter as necessary. Filter sand should normally last four to five years.

Moving to DE units, poor filtration often results from coagulation or solidification of the DE If you observe hardening of the DE cake, remove and clean the elements per the manufacturer’s instructions and recharge the filter with fresh DE. If DE. is fed to the unit by a slurry feeder, the unit may not be feeding enough DE into the filter to adequately coat the septa. Conversely, an inconsistent filter cake may result from feeding DE too quickly into a skimmer when recharging the system. The trick here is to observe DE introduction rates and adjust them as needed.

More can go wrong in coating a DE filter: If you have an over-rated DE filter or an under-rated pump, for instance, there may be inadequate pressure within the filter to properly coat the septa. Here, you need to check the manufacturer’s specs and replace equipment as needed.· Backwashing also presents its share of troubleshooting opportunities: If this vital service function is not performed frequently enough or for adequate periods when it is performed, the media will not be cleaned sufficiently. It always pays in these cases to follow manufacturer specs and to avoid shortcuts now that may turn into headaches later on.· It also pays to watch out for in adequate or plugged backwash lines that might not be allowing sufficient flow out of the filter during back-washing. If a portion of the backwash discharge is retained in the tank because of inadequate flow, the back-wash line will clog over time with caked media. To address this possibility, check the lines for clogs and clear as necessary. Last but not least, a specific tip for cartridge filters: Poor filtration without a rise in pressure may indicate torn or worn out cartridges that are simply allowing water to pass through without filtering. Replace these cartridges as needed.

Symptom: Low flow rates in the system. A flow meter is a handy diagnostic tool in evaluating filter performance. If you get a low reading with a flow meter but a high reading on the pressure gauge, something is restricting the flow — most likely a blockage in the piping that must be ferreted out or, possibly, under sizing of the entire piping system. As a rule of thumb, the maximum flow rate through a 1-1/2-inch PVC pipe is 70 gallons per minute. Through 2-inch plumbing, it should be 110 gpm. These figures are based on a standard hydraulic specification of an eight-feet-per-second maximum velocity.

A drop in the return tow may be traced to a clogged pump strainer basket or skimmer basket. The remedy here is simple: Clean the baskets. Clogged impeller vanes will also reduce the return flow. In this case, disassemble the pump and clean the impeller.

If both flow and pressure readings are low, the pump may be undersized— or you may have a plugged pump impeller or lint trap. it is important to note that pump or motor trouble can lead directly to filtration problems.

symptom: sand or DE. entering the pool.
the first suspect with sand -or- DE. clouded water is the backwash valve: if it is left in an intermediate position, media can flow back into the pool. if this obvious answer doesn't suffice, you'll need to look for solutions inside the tank. with sand filters, broken laterals are a common culprit here--and replacement is the only solution in a DE. filter torn or worn out septa will let DE. flow into the pool.

If you are unable to perform immediate repairs on a sand or diatomaceous earth filter equipped with a multiport valve, the following tip may come in handy: manual feeding of chlorine or other sanitizers will maintain clean water for seven to ten days, depending upon bather load and other such factors experts suggest you turn the multiport valve to the "recirculate" position, which will keep the skimmers working as well as the automatic chlorinator, if the pool is equipped with one. the water clarity may suffer a bit, but with sufficient sanitizer, it should not turn cloudy or green. The nylon mesh on the septa can be repaired. depending on how large a hole or tear is present. And think small: A hole the size of a pencil lead will allow DE to escape.

A special tip: Always check the points where the mesh is sewn to the frame of the grid: Even slight unraveling or separation will allow DE to enter the pool. Excessive flow rate through the filter can also force sand or DE into the pool. Again, filter and pump sizing should be checked.

Symptom: Air pressure build-up. Air present in the filter tank may allow some of the filter media to be forced into the pool and can otherwise compromise filtering action. In sand filters, it’s a prime suspect in channeling; in DE units, it may disrupt the filter cake.
More important, however, air pressure build-up in a filter is dangerous. Anyone who has seen a filter fracture knows the potential for damage and possible injury·

If you have a problem with air in the tank, check for any hairline cracks or leaks in plumbing connections on the suction side of the pump. A low water level in the pool is another suspect: Air may enter through the skimmer.

It is always important to release any air present in the filter tank. (Note: Many filters are equipped with automatic venting devices.) Not only will the presence of air inhibit good filtration, it can also increase the danger of the filter tank suddenly cracking by rapidly increasing pressure within the tank.

Air is easily released by opening the pressure release valve and allowing the air to escape. When a steady stream of water comes out or the valve, then you have released all of the trapped air.

Diatomaceous earth filter perform the same water cleaning function as sand and cartridge filters, doing their job with great effectiveness so long as too much dirt, and debris haven't built up to clog the system.

At cleaning time, however. differences among these filter types become amply apparent. Unlike a cartridge filter, which requires simple hosing off, soaking or routine replacement of cartridge elements. or a sand filter, which for most part requires only periodic backwashing, a DE. filter needs to be en apart, cleaned and recharged least once each year And it’s a dirty job, no matter how much it helps the overall pool-maintenance task.

Somebody’s got to do it
"To tell you the truth, I really don’t like to split and clean D.E. filters — it’s a dirty job." says Stan Zielinski, owner of Zee’s Pool Service in Temple City, Calif.
Still, he says. ‘We do it every year religiously for all of our accounts cause I believe its critical if you want to keep your pools in good shape. I consider the filter the heart of I system. Without a clean filter, the pool will be impossible to maintain.

Zielinski also sees filter recharging as a good way to generate income.' It's a simple job. a no-brainer " he says. even though it is relatively time-consuming. But once you have the routine down, he notes. you can profitably recharge several in a day Surprisingly, however. Zielinski and other technicians report there are many in the service industry who don’t charge extra for the work, instead including it as part of the regular service package." I think a lot or techs who don’t charge extra for the recharging service are really missing an opportunity to make some extra money," he says. "It’s the kind of job that most homeowners don’t want to get into, so it only makes sense to be paid for your trouble. The going rate?" We're up to $40 per filter," Zielinski says," and I know a lot of people who are up to $50 or $60." 

Heavy action in the tank
Bather load and a host of other factors air-bourn debris, algae conditions and the like are critical factors in determining the need for recharging. Given proper periodic backwashing, however, D.E. filters can go for a long period of time between recharging.
Indeed many technicians handle the task on an as-needed basis, just keep an eye on backwashing as the time between backwashes decreases and/or as water clarity deteriorates, recharging is in order.

Other technicians, however, simply schedule their D.E. filter recharging on an annual basis. most who employ this strategy-Zielinski among them-say it's best to do it in the slow period before the season starts. this timing also serves to prepare your pools for the heavy bather loads of summer.

The tool chest for D.E. filter work in small: You'll need a regular screwdriver, pliers, open-end wrenches, channel locks, a bucket and a high-pressure hose nozzle along with replacement 0 rings and a bag of filter medium. last but not least, you might consider bringing along rubber boots and a work bib ,unless ,that is, you don't mind getting D.E.-and the gunk it has collected -all over your clothing.

It's also a good idea to bring along some spare parts -extra grids, clamping devices and manifolds just in case something has gone awry between charging. Zielinski also suggests keeping a water-tight plastic trash can on hand in case you need to soak an excessively dirty grid.

It also pays to be technically prepared: before getting into the task, consult the filter manufacturer's literature for specific service routines.

A final consideration: many cities and countries have specific regulations controlling the disposal of spent D.E., some even requiring that the dirt be stored in a container and disposed of at a designated location. to avoid legal entanglements for yourself and your customer, get up to speed with local ordinances; a quick call to your local health department should give you the information you need.

The joys of modular maintenance 
The basic design of cartridge filters makes them a snap to service. Here’s a step-by-step guide to getting the job done correctly — first time, every time.

Servicing cartridge filters is no sweat: All you do is simply remove the cartridge elements, soak them, hose them off and then put them back in place.

In fact, if there’s any burden placed on service routines by cartridge filters, it’s because cleaning or replacement of the elements are the only options for cartridges. Unlike sand or diatomaceous-earth filters, cartridge filters cannot be cleaned by backwashing. As with all types of filter media, you can determine the need for service with cartridges by watching the internal pressure rise. As a rule, when it hits 8 to 10 pounds per square inch above the baseline pressure — which you should mark on the face of the pressure gauge with a grease pencil or note in your records or on a route sheet it’s time to swing into action.
In caring for a cartridge filter, it’s useful to keep in mind that after you’ve cleaned the cartridge one or two times, you won’t fully recover all of the filter surface, particularly with an older-model cartridge. Estimates do vary on the recoverable surface, but many experts say you’re likely to retain about 65 to 75 percent of the filtering capacity after each cleaning.

As a consequence, in pools with heavy bather loads or other conditions hostile to effective filtration, some technicians simply prefer to replace cartridges rather than bothering to clean them. This, of course, is a judgment call, but if you do decide to make a habit of automatically replacing elements, be sure to factor the cost of new cartridges into your pricing. Because thorough cleaning typically requires overnight soaking (depending on the type of cartridge you’re working with), you’ll also need to consider what to do with the client’s equipment while the cartridge is out of commission. You can either leave the system off, which means you’ll have to return to the jobsite the next day, or you can have a spare set of elements to use as replacements at each cleaning, rotating each set from the filter tank to the soaking bucket.

In discussing cartridge-filter care, it’s important to note that this kind of filter has come a long way in recent years. Advances in cartridge design, internal-flow characteristics of the tanks and improvements in the filtering materials themselves have all resulted in greater time between cleaning— in some cases as long as a year — and dramatic decreases in the size of filterable particles —sometimes as low as 3 to 5 microns.
Proponents of cartridge filtration say that these improvements have greatly cased the maintenance burden and bolstered water quality and clarity in pools and spas fitted with these new systems.

To help you keep the cartridge filters operating in tip-top shape, the following pictorial illustrates the basic techniques For typical cartridge service and replacement. As always, you should consult manufacturer literature for specific maintenance procedures and don't forget to release air pressure From the system when restarting the circulation system!

Backwashing is the word when it comes to regular service for high-rate sand filters. Unlike diatomaceous earth or cartridge filters — which must be opened for periodic cleaning and replacement of media — a sand filter can go almost indefinitely without needing fresh sand. The basic physics of sand filtration are also different from rival filter varieties: High-rate sand filters clean water via a process known as depth filtration, meaning that dirt penetrates the sand bed and is captured in the tiny spaces between grains of sand, By contrast, dirt and particulates are captured on the surface of the media in both cartridge and DE filters. The depth-filtration principle works just fine — unless, that is, the sand filter is not backwashed often enough. Without backwashing, dirt particles begin to accumulate on the surface of the sand bed and will result in short cycles, channeling, and poor overall filtration.

Conversely, if you backwash too often, you will also compromise filtration: When the sand bed is totally clean, some of the smaller particles of dirt will pass through unfiltered, As the bed begins to accumulate dirt, the filter begins to catch those smaller particles. In other words, getting ahead of yourself by cleaning the media too often will prevent a sand filter from doing its job

Keeping up with dirt
How do you know when it’s time to backwash? One obvious cue is cloudy water: When the pool gets murky, a dirty filter is the prime suspect. Another, far better cue, however, can be found with the filter’s pressure gauge or gauges. If the system has both inlet and outlet pressure gauges, you will note only minor pressure differentials perhaps 3 psi — when the filter media is clean. As the sand bed begins to load up with dirt, that differential will begin to increase. In most high-rate sand filters, it’s time to backwash when the pressure differential reaches 18-20 psi.

If the system has an inlet pressure gauge only, you should backwash when the pressure increases by 8-10 psi from initial post-backwash readings. The best idea here is to mark the pressure gauge with a grease pencil right after a good backwashing—or to maintain a record of the running pressure on a route sheet as you monitor filter cycles.
These filter cycles can be affected by many different factors, ranging from heavy bather load and algae to wind-blown dirt and debris, In addition, a sand filter on a newly plastered pool will clog quickly with plaster dust, which often precipitates out of new plaster during startup procedures.

This fine plaster particulate can easily clog a sand bed and greatly reduce the length of initial cycles. In fact, when first starting a sand filter on a fresh pool, it may be necessary to perform an extended backwash of two to three times the normal duration to rid the sand bed of the bothersome dust.

Routing the flow
Backwashing is a simple matter of reversing the flow through the filter by sending water up through the under drain or laterals and diverting the outlet water to waste. The procedure is simple: Turn off the pump to avoid damage to plumbing or valving, then turn the control valve to the backwash position and restart the system. Once the filter has been backwashed for the desired time. shut the system down and reset the valves, Don’t fire up the system right away: The sand bed needs time to settle back down into place. When you restart the pump, a small burst of cloudy water may enter the pool. This is typically caused by a residue of backwash effluent present in the sand bed as a result of inadequate backwash time. Some valve arrangements dodge this problem by sending a small initial burst of water to waste before returning filter effluent to the pool.
Given a typical flow rate of 15-20 gpm per square foot of filter area; most manufacturers recommend  backwashing for 2-3 minutes. As always, it’s a good idea to consult manufacturer service manuals for specific backwashing procedures.

Putting sand to bed
The beauty of a sand filter is that the sand itself acts as a permanent medium: Once it’s charged you will rarely — if ever —need to replace it. The keys to that longevity are steady backwashing routines, as described elsewhere in this article, and getting the system off to a good start with proper charging.

Here are the basic steps: First, obtain sand of the proper size. Most sand filters use filter sand, which is typically .45-.55 millimeters in diameter. It is also commonly referred to as "pool grade #20 silica sand." (Note: some filters also use gravel in the filter bed. Consult manufacturer literature for proper gravel specifications)

Next, to keep sand out of the circulation system, cover vertically exposed plumbing or standpipes with some type of protective cap such as a coffee or soup can. On some models, you also will need to position tube lateral assembly in the tank before adding  the sand to ensure that internal plumbing seats properly when the valve at the top of the filter dome reassembled.

Just before adding the sand some manufacturers recommend filling the bottom of the tank with a few inches of water to act as a cushion for the sand as it is poured into the tank. This will help prevent damage to the lateral assembly.

Pour the sand gently through the top of the filter tank. Although different models require varying amounts of sand, a good rule of thumb is to leave 10-12 inches of freeboard that is, the space between the top of the sand bed and bottom of the diffuser assembly.
Adequate freeboard will prevent sand loss during backwashing. Conversely, if the sand bed is too shallow, the filter will work but will load with dirt quickly and requite frequent backwashing.

Service and installation manuals offer various tips to help you charge the filter Some, for instance, recommend holding down the vertical standpipe to make sure it isn’t dislodged as the sand is being added.

Remove the protective caps and replace the top valve or dome on the top of the filter tank. Some assemblies are threaded into the top of the tank, while others are held in place by a clamp assembly All assemblies use 0-rings to create a good seal, with manufacturers typically recommending use of an appropriate 0-ring lubricant to ensure a good seal.

a sand fitter, you must make certain that additional sand will not displace the lateral assembly which must align with the top assembly on the tank. damage to the lateral assembly. When you look at a pool equipment pad, you see only a filter’s external expression: the tank, some valves and a bit of associated plumbing. But there’s a lot more going on just beneath the skin. where suppliers are working to maximize performance and ease maintenance through use of new and different materials and technologies.

For years now the pool and spa industry has relied on a familiar trio of filtration media. Yes, variations on the basic themes of sand, diatomaceous earth and cartridge systems have emerged periodically, but for the most part, the three systems have enjoyed consistent, widespread use and success in the United States and around the world, But that may now be changing: In recent years, new approaches to filtration technology have given service technicians, builders and consumers a broader set of options to consider. In some cases, these developments have taken the form of new materials used as the filter medium—materials that serve as direct replacements for existing products. In others, the medium itself is familiar, but design factors, particularly with respect to system hydraulics, have enhanced standard product performance. To keep you up to date, let’s take a look at what’s new on the equipment pad when it comes to pool and spa filtration,

For years, DE filters have won esteem for the quality of filtration they are capable of delivering. Indeed, the powdered remains of the fossilized diatoms that make up this medium can remove particles as small as 3 to 5 microns inside — the best basic rating available among the three common media types. Filtration at that low-micron level enhances water clarity and even removes certain types of algae spores.

For all its power however, DE has a "dark side" that vexes many of its users: An inert substance, DE is not biodegradable and is said to adhere to and thereby clog sewage piping and storm drains. Further, there is evidence that inhaling DE particles over extended periods of time can contribute to respiratory problems among those who scoop the dry material out of bags and into skimmers. These concerns have caused a variety of regulatory agencies to damp down on rinsing or backwashing D.E. grids into storm drains and gutters, among other restrictions. So technicians working with DE filters are finding themselves facing new ordinances—and much more energetic enforcement.

The potential with D.E. for trouble down the road has led some suppliers to investigate alternative media that work with the same basic tanks, grids and technology used in D.E. filters. One candidate here is cellulose fiber, the main ingredient in paper pulp and a common food additive. Currently offered by several distributors throughout the country and available to the pool and spa industry as a filtration medium since 1992, this powdered material can be used as a direct D.E. replacement. Its proponents claim equal or better filtration compared to D.E. —as low as two microns. And because it is a completely nontoxic, biodegradable substance, it can be used without any of the headaches associated with D.E. use and disposal.

"As an industry, we don’t want to lose the level of performance we get from D.E. That’s not an issue with cellulose fiber," says Dick Jameson, owner of SWIM, a Santa Ana, Calif.-based distribution firm that markets a cellulose-fiber product. "The beauty of cellulose fiber is that it is already used in the food industry as an additive and is FDA-approved." You could eat it if you wanted to," he says, "so there aren’t any of the regulatory concerns you have with D.E.’

Another advantage is that cellulose fiber is used the same way as D.E. It forms a slurry, is added to the system through the skimmer and forms a cake on the filter grids as it flows through the tank, As with D.E., the material loads with dirt and is backwashed to waste once the internal pressure in the filter tank increases by 10 to 15 psi. there are, however, some key differences. For starters, less cellulose fiber is required to create the filter cake. "When we first began testing the product, we started out with a one-for-one replacement dosage," reports Jameson. "We learned very quickly that it took much, much less cellulose than D.E. "In fact, after two years of experimentation and field testing, he now recommends using just one-eighth the amount of cellulose fiber compared to D.E. "That really takes some getting used to," he reports, "because there’s always a tendency to think more is better," There's a learning curve that someone using the product needs to go through," observes Jameson "But it’s simple: If you’re putting in eight coffee cans of D.E. now, it can be hard to put in just one or two. Your mind keeps telling you that you need to put in more."

Another point cellulose fiber has working in its favor is its ability to act as a filter aid in sand and cartridge filters. In both cases, it enhances filtration by removing smaller particles than sand and cartridges generally do — including some types of algae spores. That's where we’ve really seen the most benefit" says Jerry Wallace, a service technician and co-owner of Swim Chem. in Sacramento, Calif.

"We’ve used it on some of our problem pools that have sand and cartridge filters, and we’ve been able to clear up the water really well." Another distinction of cellulose fiber is its ability to trap oils far more efficiently than D.E. That’s good in some applications, but on its own in high-use and commercial pools, cellulose fiber’s oil-absorbing ability causes the filter to gum up more quickly, resulting in short cycles between backwashing. Because of that, says Jameson, "We recommend that you use an enzyme product when you use cellulose Fiber, When you use an enzyme to break down the oils you end up with outstanding water and longer cycles" Agrees Mark Machesney, water features manager for the Phoenician a resort hotel in Scottsdale, Airs,, "It’s increased our filter cycle on our main pools by days. And because we use less of the product, we have less to clean up when we clean our filters."

But when it comes to systems with undersized filters or poor hydraulic characteristics, says Jameson, cellulose fibers can actually pose a problem. " Because it works so well as a filtering medium," he says, "it really tends to show you where you've got a poorly designed system, especially if it’s undersized. You definitely have to have enough filtration area, or the media will load up very quickly. in that sense, cellulose fiber is less forgiving than D.E.’

D.E. isn’t the only filtration medium for which a direct-replacement product has been suggested: Sand, too, is facing competition from a family of minerals known as the zeolites.

The term refers to a family of about 30 volcanic minerals that have been used for decades in a variety of industrial applications. The oil and  nuclear industries, for example, have used various zeolite forms to filter waste water, and a specific zeolite species — that is, clinoptilolite — has been used for about 10 years on swimming pools. little known in the United States (but on its way), the product has been marketed in the United Kingdom by British Zeolite Co. of West Sussex, The material comes in a granular Form, is extremely porous and, according to the supplier, offers filtration down to 5 microns. which makes it roughly equivalent in performance to D.E.

Indeed, asserts Dr. Alan Dyer, a fellow of Britain’s Royal Society of Chemistry and an expert on zeolites, "The efficiency of a zeolite filter medium is better than diatomaceous earth." With the use of a zeolite," he explains, "it will be possible to extend the time between backwashing. This will be of particular value to those managers of very heavily used pools that have to be hack washed daily."

In application the product works in standard sand-fitter tanks — but at roughly 65 percent of the volume by weight in most high - rate sand systems. Moreover, the product has a life cycle of five to seven years — quite similar to the performance expected with sand.

Besides capturing smaller particulates and offering longer filter cycles by virtue of the porosity of the mineral, proponents of the product make a bold claim that zeolites in general and clinop-tilolite specifically exhibit a strong affinity For ammonia. It takes a bit of doing to trigger this affinity — that is, you need to add a layer of sodium chloride to the filter bed — and the precise chemistry is quite involved, but suffice to say that the addition of 10 percent common table salt to the filter bed activates an ionic reaction that causes the mineral to remove ammonia from water as it passes through the filter.

"If the zeolite is preactivated with sodium ions," says Dyer, "it will absorb very large quantities of ammonia in its various Forms. In some commercial pools, 12 to 15 months elapse before the filter bed is saturated with ammonia.’ By taking ammonia out of the picture, he says, zeolites effectively reduce the formation of chloramines — which results in better water quality and lower chlorine demand." Since clinoptilolite will remove amnion. chlorine usage has been reduced in some pools by as much as 50 percent, although the norm is probably less than this.’ says Dyer.

"Since the chlorine demand is lower, the need for ancillary chemicals is also reduced. Less chlorine, For example, can mean less pH correction" Reports from the United Kingdom support Dyer’s view. Among the strongest advocates is John Fowler, a retired designer and builder and former president of the Swimming Pool & Allied Trades Association, the U.K.’s leading trade association."

I am happy to say that the results have been most satisfactory" he reports. "In a summer that has been hotter than any in recent years and one in which my pool has been heavily used — the water quality and clarity have been exceptional.

"I can confirm that this product has the unique property of stripping out ammonia from pool water and of reducing chloramines levels — without the need for break-point chlorination," he adds.

Some of the advancements in filtration seen over the past few years have been far more subtle than the instances discussed above — but are no less significant. Case in point: the evolution of cartridge-filter technology. Here however, the advances have not. been so much in the medium itself as in cartridge and hydraulic design and in the basic approach to Filtration.

According to their advocates, these advances put cartridges right on par with the performance of D.E. and sand." There are now systems with much greater filter area and designs with a single cartridge versus multiple cartridges," says Heidi Hansel, customer service manager for Harmsco. a manufacturer of cartridge filters based in North Palm Beach. FL. "But from our perspective, people can’t see the biggest difference unless you really know what you’re looking for."·

That difference, she says, has to do with the development of what is called technical media, a new cartridge fiber that combines cotton with polyester. This pleated material is now capable of filtering particles in the 3 to 5 micron range —a performance that results, she says, in "highly polished water." This performance far exceeds the standard of 20 to 40 microns set for cartridge filtration by the Nations Sanitation Foundation. And even though cartridge filters remove smaller and smaller particles as they load with dirt, Hansel says that her company's product is the first to remove particles so small right off the bat." You get that increased flirtation. because the cotton fibers swell when they get wet," she explains.

Another line of development with cartridge filtration involves development of larger and larger systems (some with massive single cartridges, others with clusters of smaller cartridges) with filter areas up to 450 square Feet or more —size that makes these filters contender when it comes to big commercial pool.

That’s an important point, because even though their advocates have long said cartridge systems are well suited commercial use, the common perception is that they work better in smaller settings. Mark Shirley, owner of Commercial Pool Specialists in Jupiter, Fla., says he’s been using cartridge filters on his commercial accounts since 1983. "I like the filtration capacity and I like the after market business," he says. "You get to sell your customer a new set of cartridges each year. which is nice." But mainly I’ve always been a proponent of cartridge filtration because I like the results," he says, noting the Fact that they now filter down to the 3-to 5-micron range.

"At that level, you get beautiful water and less algae. And the only time· their greater efficiency can be a problem is with some high-use pools —and in those cases it’s because the filter is actually working too well." For his part, Shirey prefers multiple cartridge systems to single-cell units "They’re easier to clean," he explains "The deep pleats on The big single cartridge Filters require a lot of effort in cleaning, and I’m not sure you ever get all of the dirt out of there.

On average, Shirey says, his crew clean filter elements every eight to 12 weeks, trading out a second, clean set of cartridges for the originals, which an hosed off and then soaked in a trisodiun phosphate solution if necessary." There's not as much work with sand filter as there is with cartridges, he observes "but you’re only getting 40 micron filtration and the water just doesn’t clear up as well. It’s as simple as that."

Another line of action on the cartridge-filtration front has involved pursuit of low-maintenance systems — an area in which Sta-Rite Industries of Warerford Wis., has engaged itself fully. For the past three years, the company has been marketing a product line using what it calls "modular media filtration.’ ‘the system features two filter modules— essentially large filter cartridges mounted one inside the other — and specially designed internal hydraulics.

With a carefully contoured tank shape and special diffusers that direct the flow of water tangentially across the filter surface rather than directly at it, the- system. says it's manufacturer, uses the entire available Filter area more effectively than standard cartridge tanks." What you have in most cartridge filters is an uneven distribution of the dirt on the filter elements," says Tom Larson, product manager for Sta-rite, "The way this system is designed, the load is evenly distributed top to bottom.’

The result of this efficiency is a filter that can handle a tremendous amount of dirt without much increase in internal operating pressure. "Our 450-square-foot system can bold 50 pounds of material," Larson says. "before, you might only get 10 pounds in there before you had to clean the filter." That increase in filtering capacity has resulted in dramatic claims about the length of the filtration cycle. "We’re talking to people who say they don’t touch their filters for up to a year,’ Larson notes. That sounds so good, he says, that he’s the first to concede it seems like an exaggeration, "but we’ve shown that it’s not," he says.

To back up its performance claims, the company has conducted extensive tests on its system What’s more, they get strong testimonials from the field, including this from Mary Wise:" We were very skeptical when we first heard about this filter," says the co-owner of Wise Pool, a construction/retail/service firm in Conroe, Texas,' But once we started using it on our customers’ pools, we were amazed.

"Even in pools with moderate to heavy use, she says, the modular-media system can indeed go as long as a year between cleanings. "And then it’s just a matter of unscrewing the caps on the filters and hosing off the elements," she says. "Anybody can do it. This system is about as foolproof as you can get." As is the case with all of the products and systems mentioned here, the Sta-Rite system represents what its manufacturer describes as all evolutionary step in filter technology. And as always, it’s left to those in the field to discriminate between the real deal and the marketing hype.

In each of the cases covered here, however, it’s reasonably easy to put the new technologies to the test: Turbidity—or the lack thereof — is a sure-fire way to size up filter performance, and ease or difficulty of maintenance routines is another. But such tests, say these suppliers, must be fair: As they observe, the best filter or filtration system in the world cannot compensate for inadequate hydraulic design or poor water chemistry. And if you’re looking to redeem a poorly designed system with a new filter, they say, you’ll probably be in for a disappointment.

On that score, says Wise, it’s a matter of watching the fundamentals. "I don’t care what filter you put on a pool: If the plumbing isn’t tight," she says, "you’re going to have problems." New products can be wonderful, but if you’re not paying attention to the basics, your pools won’t work the way they should. And," she concludes, "you and your customers won’t he at all happy with the results.

Cleaning up
To ensure and prolong the effectiveness and life span of a filter cartridge, you need to know how best to clean them. The key ,say those who supply these devices to the industry, is familiarity with three cleaning techniques:

Rinsing: Many times all you need to do is rinse the cartridge with the aid of a high pressure hose. often that is all that is required to free most of the dirt from the pleated media.

Soaking: for deeper cleaning, cartridges can be soaked in a solution of water and trisodium phosphate. this removes oils grease and other organic material imbedded in the medium

washing: if calcium has built up on the medium, you can wash the cartridge with a light acid but note: acid washing will reduce the life of the cartridge and should only be done when calcium has in fact built up on the cartridge rather than as a routine maintenance procedure.

How do you know when to acid wash your cartridges? Unicel filter cartridges, a manufacturer based in Burbank, calf. recommends the following: After you've soaked the cartridges in TSP and rinsed them off, apply a drop or two of acid directly to the pleats. If you see bubbling, then calcium is present and the cartridge could use a light acid wash. If there is no bubbling, then don't worry about it .(In the same way, they advise, you know your acid washing  is finished when the solution stops bubbling.)

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