How To Get Perfectly Balanced
There's more to taking care of
a pool and spa than just keeping the water clean. You also have to
make sure the water is properly balanced.
Water that is not balanced --
that is too acidic or too basic -- can cause bather discomfort,
cloudy water and damage to the pool and spa surfaces and equipment.
Water follows certain natural
laws, just like other things around us. Unsupported objects fall to
the ground, and this is called the law of gravity. It is the nature
of water to dissolve the things it contacts until it becomes
saturated. It is possible for it to dissolve too much and become
over saturated, at which point the water loses its excess material
by precipitation. This is governed by the laws of chemical
equilibrium, more commonly referred to as water balance
(see Table 3.a).
Many operators are already
familiar with this subject to some degree. A commonly used too] in
determining the degree of saturation in pool water is the Langeleir
Index. Originally devised for the complicated and variable
conditions found in industrial water treatment (boilers, cooling
towers, heat exchangers etc.), it has been simplified for use with
the swimming pool water. The degree of saturation by the pH,
temperature, total alkalinity and calcium hardness found in the pool
The pH reading is used
directly. The temperature factor (TF), alkalinity factor (AF) and
calcium factor (CF) are read from Table , using the test values
obtained from a pool test kit.
The constant (12.1) includes a
factor for Total Dissolved Solids (TD), assuming a value of less
than 1000 ppm TDS. When the TDS is found to be higher (1000-2000
ppm) a value of 12.2 should be used for the constant.
To determine whether the pool
water is aggressive (under saturated) or scale forming (over
saturated), the operator would
Complete the water testing
Run the Water Balance Test
from Online Water Testing
Index - Saturation Table
Index = pH + TF + CF + AF - 12.1
CF - Calcium Factor
AF - Alkalinity Factor
Hardness Expressed As PPM CaCO3
Alkalinity Expressed As PPM CaCo3
The term balancing has many meanings when
referring to pool and spa water chemistry and conditions. The
following summarizes these various definitions and conditions.
Two chemical levels exist that
determine corrosive conditions. Both conditions are serious and
costly if not checked. (1) If pH is lower than 7.0, the water is
considered acidic and it will attack and dissolve metals, especially
the copper pipes in the heat exchanger located in the pool heater.
(2) When the saturation index is a negative value, the water will
attack or dissolve the calcium found in the pool-shell plaster or
grouting between pool tile.
Both the human skin and eyes
will react to chemical extremes. There are two conditions that will
cause inflammation and irritation to the eyes. The human eye has a
pH of 7.3-7.5 and will become extremely uncomfortable when pH is
below 7.0 and above 8.0. The second condition is when the
combined-chlorine level is above .5 ppm and the chloramines cause
the irritation. Both conditions should never occur if hourly testing
is accomplished and recommended chemical levels are maintained.
Two conditions exist that
cause iron or copper metal staining of a pool shell, especially a
plaster surface. Excessive iron content in the water supply may
cause a reddish or rust discoloration at the inlets of the pool if a
chelating agent is not used to hold the metal in suspension.
Copper staining creates a blue
or blue-green discoloration of a plastered pool shell. This
condition is created when the pH is lower than 7.0 for long periods,
and the acidic water attacks the copper tubing found in the heater's
heat exchanger. This can become very costly if walls require sanding
or sandblasting and if it is necessary to replace a heat exchanger.
Water clarity is a result of
proper chemical balance, adequate circulation and filtration. Most
often, cloudy water conditions are caused by low chlorine, high
alkalinity, high pH, high TDS or a combination of these. It is
possible to have proper chemical readings and still have cloudy
water during high swimmer load if the flow rate of the circulation
system is low or if there is poor filtration.
Properly balanced or
saturated water prevents damage to the pool and equipment.
Unsaturated water corrodes plaster walls, fixtures, plumbing,
etc., and causes staining. Oversaturated water deposits scale or
becomes cloudy. o The operator needs to test and control pH,
total alkalinity, and hardness in order to maintain balanced
Proper pH control (7.2 to
7.6) ensures: (1) the proper form of carbonate alkalinity for
saturation, and (2) the proper form of HOCI for sanitizer
Soda ash is used to raise
pH. Acids are used to reduce both pH and total alkalinity,
depending on how they are applied.
Sodium bicarbonate is used
to raise total alkalinity.
Alkalinity of 80-120 ppm
is preferred for both pH buffering and calcium carbonate
Calcium hardness of 200
ppm, or more, is preferred for proper calcium carbonate
saturation and for avoiding soft-water scale found in spas and
Calcium chloride is used
to raise calcium hardness. The best means of lowering hardness
is to drain off some of the water and refill with fresh water.
To help you get a handle on
what water balance means -- and how you can maintain it -- let's
look, one at the time, at the factors that shape your water quality.
Is acting as the main
sanitizer to kill algae and bacteria in the pool water. The level
should be between 2.0 and 3.0 on your test kit. During hot weather,
high readings are better.
Available Chlorine (FAC)
All chlorine - regardless of
whether it is introduced as a gas or as a dry or liquid compound
when added to water, does exactly the same thing: It forms
hypochlorous acid (HOCl) and hypochlorite ions (OCl-).
HOCl is the killing form of
chlorine; OCl- is relatively inactive. However, together, they are Free
Available Chlorine (FAC).
Combined chlorine is formed by
chlorine combining with ammonia and other nitrogen-containing
organic compounds. Some sources of these compounds include
perspiration, urine, saliva and body oils. These combined forms of
chlorine, also called chloramines, are still disinfectants, but they
are 40 to 60 times less effective than free available chlorine.
Chloramines kill slowly, so
when they are formed in swimming-pool water, the FAC is no longer
present for "instant kill" sanitation. Free available
chlorine and combined chlorine exist together in many pools. There
are simple tests to measure the levels of each. These will be
described in detail in another chapter.
In addition to reduced
effectiveness against bacteria, chloramines cause eye irritation and
the so-called 'chlorine odor" that swimmers complain about.
Chloramines have a foul, irritating odor; free chlorine in water in
normal concentration has no discernable odor.
Simply stated, there are three types of
chlorine test readings: free available chlorine (FAC), combined
chlorine and total chlorine. Free plus combined equal total. Only
the free chlorine is effective in killing bacteria or algae. A high
level of combined chlorine indicates the need for shocking or super
chlorinating to eliminate it.
Although bromine in its
elemental form is a liquid, it is not available for swimming pool
disinfection in that form. Elemental bromine is a heavy, dark brown,
volatile liquid with fumes that are toxic and irritating to eyes and
respiratory tract. For pool sanitation, bromine compounds are sold
in two solid forms - a two-part system that uses a bromide salt
dissolved in water and activated by addition of a separate oxidizer;
and a one-part stick or tablet that contains both bromine and an
oxidizer and is dispensed by an erosion-type feeder.
The chemistry of bromine is
similar in many respects to the chemistry of chlorine; however,
bromine cannot be used for shock treating.
Bromine has a pH of 4.0-4.5.
When bromine is added to water and an oxidizer is present, the
bromine forms hypobromous acid (HOBR) and bypobromite ions (OBr).
Like chlorine, the percentage of each is affected by pH. However,
the effect is not as dramatic as it is with chlorine. Table 3.2.a
displays the effect of pH on bromine. Like chlorine, bromine
combines with organic impurities to form combined bromine or
bromamines. However, combined bromine is still an effective
sanitizer, and it does not smell. Because of this, bromine is
popular for spas.
Bromine as HOBr
Bromine as OBr-
Is the level of how acidic the pool water is.
You must maintain a good pH level or your chlorine will not work
effectively. The level should be between 7.2 and 7.6.
The most fragile and arguably the most
important component of water balance is pH, a reading that indicates
how acidic or basic your pool and spa water is.
Without going into the entire story of what pH
is and how it works, suffice it to say here that it's important to
monitor it because it has an impact on your sanitizer effectiveness,
not to mention your pool or spa's surfaces, equipment -- and you.
Here are the most common problems associated
with both high or low pH levels:
Shorter filter runs
Skin and eye irritation
Etched or stained plaster
Skin and eye irritation
Destruction of total alkalinity
|The ideal pH range for pools is between 7.4 to
7.6. For spas, the range is 7.2 to 7.8. Any reading below 7.4 for
pools or 7.2 for spas means your water is acidic.
To correct the situation, you would add soda
ash or sodium bicarbonate, two substances available at your local
pool/spa supply store. Note: You should not add soda ash to a spa as
you would to a pool -- it is too strong for the small spa
If the pH reading is above 7.6 for pools or
7.8 for spas, it means the water is basic or alkaline. To bring the
pH level down in pools, you'll need to add some liquid muriatic acid
to the water. Muriatic acid is also available in pool/spa supply
Here again, you need to take special care with
your spa: Liquid muriatic acid is too powerful for the small volumes
of water found in spas. Therefore, experts do not recommend using
muriatic acid in spas. Instead, you should add dry acid.
pH is a number between 0 and
14 that indicates how acidic or basic a solution is (See Figure
5.4). Pure distilled water has a pH of 7.0 and is neither acidic nor
basic. Water with a pH of lower than 7.0 is said to be acidic, and
the smaller the number, the more acidic the water is. One the other
hand, water with a pH greater than 7.0 is basic, and the larger the
number, the more basic the water.
Acidic compounds, such as
sodium bisulfate or muriatic (hydrochloric) acid, lower the pH of
water. Alkaline compounds, such as soda ash or sodium hydroxide,
raise the pH of water. Alkaline compounds are, therefore, basic. The
use of both alkaline and basic to refer to high pH, and to compounds
that raise the pH, causes some confusion with the alkalinity
of water. The difference between total alkalinity and pH is
In addition to the effects of
pH on the chlorination process, there is also an effect on the total
alkalinity of water. This plays a major role in the degree of
calcium carbonate saturation. This dual effect makes the control of
pH very important to the pool operator.
Molecules of water (and other
substances) break up into electrically charged particles called
ions. Water separates into positively charged hydrogen atoms, called
hydrogen ions, and negatively charged particles containing one
hydrogen atom and one oxygen atom.
The pH of a solution does not
indicate the total amount of an acid or base in the solution, but
only how much of it is ionized. This point is very important in the
subject of total alkalinity, which is explained further on in this
pH is a very complicated
subject, and the above explanation has been deliberately simplified
to give sufficient, accurate information for swimming pool
operation. Chemists would not accept it as complete, but it will do
for this discussion.
Accurate control of the pH of
swimming pool water is essential. The effects of pH upon
flocculants, bactericides, algae growth, equipment maintenance and
bather comfort will be discussed throughout the Handbook.
The pH of swimming pool water
must be kept slightly above 7.0 and must never exceed 7.8. Most
state health departments recommend that the pH of swimming pool
water be kept between 7.2 and 7.6. This range provides the best
conditions for precipitation of flocculants on conventional sand
filters and for effectiveness of chlorine as a bactericide.
Corrosive damage to pipes,
filters and pumps might result from operation at a pH below 7.0.
High pH values cause reduced effectiveness of bactericides and
encourage the growth of algae.
Pool Water Zone
- pH too low
- Chlorine Lost
- pH Ideal
- Maximum Chlorine Efficiency
- Comport Zone
- pH Too High
- Scale Forming
- Chlorine Less Effective
Control of pH is relatively
simple. pH can be raised by the addition of soda ash (sodium
carbonate, Na2CO3), sodium bicarbonate (NaHCO3) or sodium
sesquicarbonate (Na2Co3oNaHCO3o2H20)- Other compounds, such as
sodium hydroxide, can be used, but they are more dangerous to handle
and are not recommended. The carbonate ions produced by these
chemicals combine with some of the hydrogen ions and reduce the
This makes the water more basic. Soda
ash, sodium bicarbonate and sodium sesquicarbonate can be added to a
pool by dissolving the powder in water and feeding the solution
through a chemical feeder; dissolving the powder in a bucket of
water and pouring the solution directly into the pool water; or by
broadcasting the dry powder over the water surface. The amount
required varies greatly from pool to pool, and only trial-and-error
experience determines the correct amount for any specific pool.
Addition of acids, or acid
salts, causes an increase in hydrogen-ion concentration and lowers
the pH. Sodium bisulfate (NaHS04) is an acid salt that is frequently
used because it is safe to handle. It can be added by chemical
feeder or by dissolving in a bucket and pouring directly into the
pool. Muriatic acid is the commercial grade of hydrochloric acid (HCI).
If the pool operator is sufficiently aware of the dangers and
precautions of handling acids, either of these two can be poured
directly into the pool when no one is swimming. Acids may also
affect the total alkalinity of water. This is discussed in the
section on "Control of Total Alkalinity.-
The scientific definition of pH is 'the
negative logarithm of the Hydrogen ion concentration'.
First accept pH is a scale measuring the
acidity or alkalinity of a solution. Squeezed lemon and vinegar are
sour or acidic. If we drank them we would take something alkaline
like bicarbonate of soda or magnesia to neutralize the acidity in
our stomachs - in other words raise the pH. The pH scale runs from 0
(highly acidic) to 14 (highly alkaline) with distilled water being
neutral at pH 7.
Now instead of sour, lets use the term
'hydrogen ions', and instead of alkaline lets use the term 'hydroxyl
ions'. Vinegar has many more hydrogen ions than hydroxyl ions.
Conversely, soda ash and bicarbonate, being alkaline, possess more
hydroxyl ions than hydrogen ions. In summary, acids produce hydrogen
ions, alkalis produce hydroxyl ions. pH is the power (German 'potenz')
of a solution to yield hydrogen ions [H+].
One more step to go. The scale between 0 and
14 is logarithmic (pH 8 is 10 times more alkaline than pH 7 and pH 9
is 100 times more alkaline than pH 7)
Now we are back to the scientific explanation
of pH as 'the negative logarithm of the hydrogen ion concentration'.
Negative because the more hydrogen ions, the lower the pH.
is pH so important?
- The pH value affects the amount of
hypochlorus acid (free available chlorine) that is formed, and
therefore determines the effectiveness of the chlorine as a
killer of bugs.
At pH 6.5, 90% of the chlorine will be
At pH 7.5, 50% of the chlorine will be
At pH 8.0, 20% of the chlorine will be
Unfortunately you cannot run your pool at
pH 6.5 - it would acidic enough to corrode the metal fittings in
your pool circulation system and it is too far from the human
body's pH of 7.4 to be comfortable to bathe in. The compromise
is 7.2 to 7.6, preferably midpoint of 7.4. Remember, if you let
the pH drift out of this range, you will have to use more
chlorine to get adequate disinfection.
- Bather comfort. At high pH, the water will
make your eyes sting and possibly give you a sore throat
- At high pH there are two dangers.
- The danger of scale forming on your
pool surfaces, pipe work and fittings. This is because at a
pH of around 8.0, the calcium in the water combines with
carbonates in the water. Result? Calcium carbonate or scale.
- Calcium carbonate can form into tiny
particles and float around in the water giving it a cloudy,
- A low pH can corrode metals, eating away at
copper fittings and heat exchangers leaving metal oxides to
stain pool surfaces. Under certain conditions the precipitated
(particulate) metals can tint your hair, giving you a rather
dated appearance in these post-punk times!
A final note: Before adding any chemicals to
adjust your pH levels, you must first consider total alkalinity.
Is a pH "stabilizer". It helps to
keep the pH within the proper levels so that the chlorine can work
effectively. It reduces pH "bounce". The level should be
between 100 - 150.
Now that you know where your pH level should
be, it's time to consider the total alkalinity.
The most important thing to remember about
total alkalinity is that it affects your pH levels and therefore
must be tested before you do any pH testing and adjustments.
Total alkalinity and pH go hand in hand, but
total alkalinity has the upper hand.
Basically, total alkalinity is a measure of
the water's ability to neutralize acid (called the water's buffering
capacity), and keep your pH level within the proper range. This is
why you test and adjust your total alkalinity before even touching
your pH test kit.
Your goal? To keep total alkalinity readings
inside the acceptable range of 80 to 140 ppm for pools and 80 to 120
ppm for spas.
What happens if you don't? Let's take a quick
look at the problems that can result.
|Hard to change
Skin and eye irritation
Poor sanitizer efficiency
|Rapid changes in
pH or "pH bounce"
Stained, etched or dissolved plaster
Skin and eye irritation
IS TOTAL ALKALINITY ?
Closely related to pH, but the
two must not be confused. Total alkalinity is a measure of the
amount of alkaline materials in the water. This alkalinity will
usually be present as bicarbonates, but with a very high pH
carbonates and hydroxides can be present as well.
The relevance to pH is that the
amount of alkali (hardness) in the water will determine how easy it
is for changes in pH to occur.
If the alkalinity is too low
(below 80ppm) there can be rapid fluctuations in pH - i.e. there is
insufficient 'buffer' to the pH. High alkalinity (above 200ppm) will
result in the water being too buffered - it will make it difficult
to adjust or correct the pH.
By way of analogy, picture a
sphere resting on a flat surface. If the sphere moves along the
surface to the left, it is analogous to lowering the pH; if it moves
to the right, it is equivalent to raising the pH. If the sphere had
the bulk density of a balloon, very little force would be required
to move it left or right. It would require a much greater force if
the sphere had the bulk density of a cannon ball. In this example,
the increase in bulk density between the balloon and the cannon ball
is analogous to an increase in alkalinity. The increase in force
required to move the balloon and the cannon ball is analogous to the
idea of increased 'buffering'.
Total alkalinity is a
measure of the pH-buffering capacity, or the water's resistance to a
change in pH. This ability to resist change in pH is due primarily
to the presence of the family of carbonate ions, but certain other
compounds also provide buffering.
The carbonate ions have a
special role in water saturation. The operator must control both the
amount of carbonate alkalinity and the pH to provide enough calcium
carbonate to saturate the water without having so much that scale
Total alkalinity and pH
are related in water saturation (or balance) because, at low-pH
(acidic) conditions, all of the carbonate ions are converted to
bicarbonates. There is no calcium carbonate formed, and water
becomes aggressive to the pool walls and equipment. At high-pH
(basic) conditions, too much carbonate is formed, and even the
smallest amount of calcium ion present precipitates, causing cloudy
water or scale. At normal pool pH conditions (7.2-7.6), most of the
carbonate ions are in the bicarbonate form to provide buffering.
Small amounts of carbonate ion are present to provide calcium
Total alkalinity is measured
with a pool test kit, and, for all practical purposes, is equal to
the carbonate alkalinity. Total alkalinity may be used directly to
get the alkalinity factor (AF) for the Langelier Index.
A possible exception is when
the total alkalinity of the pool water is less than 80 ppm
and the cyanuric-acid (chlorine stabilizer) level is over 60
ppm. If both these conditions exist, the operator should determine
the carbonate alkalinity (CA) by subtracting one-third of the
cyanuric acid (stabilizer) level from the total alkalinity. If, for
example, the operator finds a total alkalinity (TA) level of 75 ppm
and a stabilizer or cyanuric acid (CYA) level of 90 ppm, before
calculating the saturation index the following correction should be
Carbonate alkalinity = Total
alkalinity - 1/3 Cyanuric acid
or: CA = TA - 1/3 CYA
Carbonate alkalinity = 75 ppm - 90 ppm / 3 = 45 ppm
The alkalinity factor from the
Langelier Table or Saturation Index Table will be 1.7 (at 45 ppm)
not 1.9 (at 75 ppm). If these conditions existed for pool #2 in the
examples given earlier, the water would be very aggressive (SI =
-0.5 instead of the -0.3 shown), and the operator should take
corrective action immediately to avoid corrosion damage to the pool
At normal-to-high total
alkalinity, there should be no need for a correction, and the total
alkalinity test result can be used both as a measure of the pH
buffering and the carbonate alkalinity in determining the degree of
Water hardness is a
concentration of the calcium and magnesium in your pool and spa
water but is often referred to simply as calcium hardness.
The amount of calcium hardness
your water will have varies depending on your water source. Well
water, for example, has a higher mineral content -- or is harder --
than a fresh-water source that has gone through a treatment plant.
Note: You do want your water
to have some level of hardness. If it's too soft, the water will
slowly but surely dissolve the plaster and any metal in your pool
and spa equipment. If there's too much hardness, you'll see scale
formation on the walls and the water will take on a cloudy
IS CALCIUM HARDNESS ?
Calcium hardness is the amount of dissolved
calcium (plus some other minerals like magnesium) in the water. The
word dissolved is important - if you can see calcium scaling up the
pipe work or the surface of the pool, it is no longer dissolved - it
has stolen a march on you. Too much calcium means cloudiness and
scaling up, too little could lead to the water satisfying its
appetite for calcium by taking it from your grouting.
The term "water
hardness" originated with the use of soap for laundering and
cleaning. Certain ions in water combined with the chemicals in soap
to form a solid precipitate, or scum, and made it hard to get soap
to lather. Thus, water with more than 100 ppm of hardness ions was
called hard water. The hardness ions are primarily calcium
and magnesium. Sometimes, such others as iron and aluminum are also
included but are often neglected because they are easily removed in
the water-treatment process. With the development of detergents, the
problem of hard water in laundering was greatly reduced, but the
term is still commonly used.
Because calcium ions combine
with carbonate ions to form the calcium carbonate needed for water
saturation, it is important that the calcium level be closely
monitored. Therefore, the pool operator needs to measure the calcium
hardness to determine the calcium factor (CF) for the Langelier
Index. The method for determining calcium hardness is given in the
chapter on pool water testing.
Like pH and alkalinity,
calcium hardness affects the tendency of water to be corrosive or
scale forming. It also appears to affect the kind of scale formed.
When a calcium carbonate precipitate occurs in soft water, the scale
particles are large and coarse. This is seen in many tap water pipes
where the local water treatment plants soften the water to 100 ppm
Hard water, however, appears
to produce a protective scale that has smaller, finer particles that
prevent corrosion. Thus, the pool operator should test and maintain
calcium hardness at 200 ppm, or higher, both to provide sufficient
calcium ion for saturation as calcium carbonate (50 ppm minimum) and
to ensure that, if a scale forms at all, it is the less harmful form
(200 ppm or more).
The acceptable maximum calcium
hardness depends on the amount of total alkalinity needed for pH
buffering. If a particular pool tends to change pH rapidly, higher
total alkalinity (over 100 ppm) is needed. Calcium hardness should
not exceed 400-600 ppm, depending on the pH and temperature of the
water. The exact values can be calculated using the Langelier Index.
Some pools tend to have very
little pH drift and can use a lower total alkalinity (less than 100
ppm). Under these conditions, calcium hardness may reach 800 ppm, or
more, without causing cloudy water or scale formation. Again, all of
the factors for water saturation must be considered in determining
the proper level to maintain.
Calcium hardness is increased
by the addition of hydrated calcium chloride, a readily available
form of calcium salt. Use 10 pounds of calcium chloride (80% CaCI2)
for each 10,000 gallons of water to raise the calcium hardness 80
The only convenient way to
reduce calcium hardness, however, is to remove some of the pool
water and replace it with fresh water. Very often, normal splash-out
by swimmers and filter backwash procedures remove enough water to
maintain an acceptable calcium level. With high temperatures and
excessive evaporation rates, additional water may have to be drained
periodically to lower calcium hardness levels.
By definition, TDS is
absolutely everything dissolved in your pool and spa water, from
metals to chlorine to alkalinity to sulfates and salts. The
acceptable range of TDS in a swimming pool is between 1,000 and
2,000 ppm. For spas, the level is 1,500 ppm above your start-up TDS.
If you have a problem with TDS,
your pool or spa water may taste salty or it may have a tint to it,
although there isn't any clouding. You might also see algae growth
and get false test readings, among other things.
If you suspect your water's
TDS is too high or low, call a professional service technician or
take a water sample to your pool/spa supply store's water lab for
further tests -- and some advice.
By now, you should have read
the basic definitions of the different chemicals and substances
found in your pool and spa water. And while keeping the upper hand
on them doesn't require a Ph.D. in chemistry, it does call for
Your ultimate goal is to reach
and maintain a certain level of sanitizer and a certain water
balance. That is, you want to keep all your chemical readings within
their proper ranges.
Here's a quick rundown of the
||1.0 - 3.0 ppm in pools, 1.5 - 3.0 ppm in
||2.0 - 4.0 ppm in pools, 3.0 - 5.0 ppm in
||7.4 - 7.6 in pools, 7.2 - 7.8 in spas
||80 - 140 ppm in pools, 80 – 120 ppm in
||200 - 400 ppm in pools and spas
|Total Dissolved Solids
||1,000 - 2,000 ppm in pools, 1,500 ppm
above your start-up TDS in spas
IS TOTAL DISSOLVED SOLIDS ?
This apparent contradiction in terms refers to
conductive chemicals that can accumulate in the pool particularly
when the water evaporates, or when the pool is not 'diluted' with
sufficient fresh water. You cannot see them because they are
dissolved, but this does not stop them corroding metal parts (pumps,
pipework, filters) on account of their conductivity. They are mostly
made up of chlorides and sulphates. Chlorides can accumulate with
long term use of sodium hypochlorite. Regular addition of alum based
clarifiers (aluminum sulphate) and dry acid (sodium bisulphate) can
increase sulphate levels. Periodic backwashing and water replacement
are the best ways of controlling TDS
High TDS - at 1,500 ppm above water-supply
level - can reduce chlorine efficiency by as much as 50%. High-TDS
water tastes salty and offers a dull appearance. High TDS is common
with spa water with high bather load, high chemical needs and a
relatively small volume of water. Outdoor pools in the Sun Belt area
of the United States that experience a high volume loss of water due
to evaporation can be plagued with high TDS, especially in shallow
pools. Splash-out, carryout and frequent backwashing offer a natural
prevention of high TDS because of dilution. TDS can only be
corrected by dilution of water with low TDS. Sea water has an
approximate TDS of 35,000 ppm, while drinking water can range
between 100-300 ppm.
Forms a protective bond around the chlorine,
making it more resistant to being burned off by the sun. Makes
chlorine tablets last longer. Pools should be stabilized whenever
large amounts of fresh water are added. The level should be 35 ppm
and is adjusted by adding Stabilizer Conditioner. Usually Cyanuric
Acid is used as Stabilizer.
IS CYANURIC ACID ?
Chlorine in outdoor pools must
be shielded from the degrading effects of the sun's ultraviolet (UV)
rays. Cyanuric acid is used in outdoor pools with the inorganic
chlorines such as calcium hypochlorite, sodium hypochlorite, lithium
hypochlorite and chlorine gas.
It is recommended that the
cyanuric-acid level be 30-50 ppm with a maximum of 100 ppm and a
lower limit of 10 ppm. The level of cyanuric acid is reduced by
dilution due to filter backwashing, bather dragout or dumping. To
meet health codes, pools above 100 ppm need to be drained of about
20% of volume, and fresh water added. Four pounds of cyanuric acid
will offer a reading of 50 ppm in 10,000 gallons of water. Cyanuric
acid has a pH of 4.0, and if added to a gas-cblorinated pool, the
addition of one-third of a pound of soda ash per pound of cyanuric
acid is recommended.
'Chlorine Lock,' a term given
to a condition once thought to be produced from high cyanuric-acid
levels tying up free available chlorine, has been proven false by
the industry. Generally, high cyanuric-acid levels of 400 ppm or
higher are associated with excessive Total Dissolve Solids (TDS) or
combined chlorine or cbloramines and not "Chlorine Lock.'
- Good water chemistry can only be achieved when all four
chemical levels are kept constant. Good Alkalinity helps keep the pH
in the right range so that the chlorine can do its job properly.
Stabilizer keeps more of the chlorine in the water instead of being
wasted ! The result? A crystal clear pool!
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