Water Chemistry & General Operations
CHLORINE, ITS PURPOSE AND
Disinfection is the most important single
factor in maintaining a pool which is safe and healthful. Chlorine
is the most widely applied disinfecting agent for swimming pool
The most common form of chlorine for home
swimming pool consumption is calcium hypochlorite containing 70%
available chlorine. This solid, white material is available as
either a free flowing powder, or tablets. Both types have excellent
stability under all normal storage conditions. In use, this material
dissolves quickly, releasing free available chlorine which is needed
to kill bacteria.
Pool water should always contain 0.3 to 0.6
parts per million(ppm) chlorine. This chlorine residual may be
achieved by adding one ounce of granular calcium hypochlorite for
each 5,000 gallons of pool water. In order to be sure that the pool
water contains the proper amount of chlorine it is necessary to test
periodically using an ortho tolidine test set which is available at
There are a number of factors which affect the
rate at which chlorine is consumed in the swimming pool. Chlorine
dissipates more rapidly in warm water than in cold water. Ultra
violet light (sunlight) causes an increase in the rate of
consumption as does the presence of organic matter such as
perspiration and bacteria that are carried in on bather’s skin
also increase the amount of chlorine needed to maintain an adequate
chlorine residual. For these reasons, it will be necessary to add
more chlorine on sunny hot days and when there are more people in
the pool than when the opposite is true.
Calcium hypochlorite should be added to the
water by means of a chemical feeder or a dispensing basket. If
tablets are used, it is important to remember that they may bleach a
spot on the floor of the pool if they are permitted to rest there
and caution should be taken to make sure that they are beyond the
reach of children who may place them in their mouths. NEVER MIX
CHLORINE WITH ANY OTHER CHEMICALS and be careful to use a clean dry
measuring device when handling this material since any contamination
may result in a chemical reaction which may cause fire.
Chlorine should be added to the pool
approximately 15 minutes prior to swimming. Tests for the presence
of a chlorine residual should be made frequently and additions of
chlorine made as needed so long as there are swimmers in the pool.
ALGAE… ITS APPEARANCE,
CAUSE and DESTRUCTION
Algae are very tiny plants that grow in
untreated water. The air contains millions of algae spores which
either settle into the water or are carried in during rain storms.
Once present in water they may be recognized initially, by the
formation of slime on the sides and floor of the pool developing
into a general cloudiness in the body of the water accompanied by a
sudden increase in the pH. In the advanced stages of growth, they
take on a green color and, if allowed to progress further, will take
on a brownish color and emit obnoxious fish type odors. Intense
sunlight is very conducive to algae growth by causing increased
water temperatures and more rapid loss of residual chlorine.
It can be said, as a general statement, that
algae growths will not develop where the proper chlorine residual is
maintained at all times. However, it is most difficult to maintain
the proper chlorine residual at all times since intense sunlight and
increased water temperatures increase the consumption of chlorine
therefore making it more expensive to control the growth of algae.
Should algae be allowed to gain a foothold in the pool,
"shock" treatment is often necessary to remove the growth.
This consists of applying from five to ten times the usual amount of
chlorine, when the pool is not in use. Allow the chlorine residual
to settle back to normal before resumption of swimming.
While chlorine may be considered an effective
algaecide, it should be apparent from previous discussion on this
subject that in order to be effective, it must be present. Since the
conditions under which algae grow most rapidly are precisely the
same as those under which it is most difficult to maintain an
adequate chlorine residual, it has become common practice to employ
algaecides to control the growth of algae leaving the chlorine free
to act on bacteria.
Another factor in favor of algaecides is that
most algae require much higher concentrations of available chlorine
than do bacteria for the same degree to kill. There are many types
of algaecides in common use the most popular of which are the
quaternary ammonium compounds and copper based products. Most
quaternary ammonium compounds are in liquid form and, since they
tend to decompose rapidly, frequent additions are required in order
to maintain the proper active residual. On the other hand, copper
based products are predominantly granular inform and require only a
single application in a given volume of water with occasional
additions to compensate for dilution due to addition of new water.
pH, ITS IMPORTANCE AND
Just as an inch is a measure of distance, so
pH is a measure of acidity or alkalinity. We know that lemon juice
is acid and that lye is alkaline, but to help us express numerically
just how acid or how alkaline, we use the pH scale.
The pH scale runs from 0 to 14. A pH reading
between 0 and 7 is on the acid side. A pH of 7 is neutral, and pH
readings between 7 and 14 are alkaline. The pH of swimming pool
water should be controlled within the range of 7.2 to 7.8.
Water that is decidedly acidic or alkaline is
uncomfortable to the bathers. Irritation to eyes and mucous
membranes, vague skin discomfort, and bleaching of hair and swim
suits is usually caused by improper pH. Human beings feel
comfortable in a relatively narrow pH zone (7.2 to 7.8) and it is
fortunate that the effectiveness of chlorine is greatest in this
Pool water which is acidic (pH below 7) is
corrosive to filters, pipes and other metal fixtures and will result
in excessive chlorine consumption. Overly alkaline water (pH above7)
tends to form unsightly whitish deposits called "scale"
which adhere to pool fixtures. In this alkaline range, the
effectiveness of chlorine is greatly reduced.
CONTROL OF pH
Adjusting the pH of water is a simple matter.
To raise a pH which is below 7.2, soda ash or pH positive powder or
briquettes must be added. To reduce a pH which is above 7.8,
muriatic acid or pH negative powder must be added.
Swimming pool water is considered hard when it
contains dissolved solids in amounts which are objectionable to
bathers, equipment, or appearance. Calcium, magnesium, iron and
manganese are the chemicals which are the chemicals which are of
primary concern. These minerals enter the pool in the water supply,
and may also be picked up from piping and pool accessories used in
the pool system.
The presence of calcium and magnesium
contribute to white cloudy water while iron and manganese usually
cause colored water.
Most hard water conditions can be alleviated
through the addition of water softening agents. Cloudy water
conditions caused by calcium and magnesium are usually the result of
too high a pH and may be easily corrected by adjusting the pH to
between 7.2 and 7.8.
Well water or ground waters usually contain
high percentages of iron and manganese. Pool waters which contain
these minerals may not initially appear to have any color, but upon
addition of chlorine, they may be oxidized and will appear as a
yellow to brownish color. Colored waters may be eliminated by the
addition of water softening agents or by the proper use of alum.
CARE AND MAINTENANCE
There are several types of filters available
for swimming pool water. Sand and gravel, diatomaceous earth,
anthracite, and cartridge types are the filter mediums most commonly
employed. Regardless of the medium used, the basic principles are
the same. This consists of passing water through tiny passageways.
Particles larger than these passages are trapped and thereby
separated from the main body of the water. This process continues
until all of these passageways are blocked. The filter must then be
cleaned and the cycle repeated.
A filter is designed to remove sediment and
suspended matter from the main body of water, however, some dirt
will inevitably settle to the bottom of the pool during periods when
the filter is not in operation. The only way for this sediment to be
removed is through vacuuming.
The swimming pool vacuum operates in a similar
manner to the common household unit except it draws water through
the vacuum head instead of air. There are two ways in which this may
be accomplished. One method employs a jet of water supplied by a
garden hose to power the suction which draws the dirt into the head
to be trapped in a cloth bag. The other method uses the suction
power supplied by the filter which draws the sediment and dirt from
the pool floor for removal through the filter. When there is a
considerable amount of sediment to be removed the filter valves
should be adjusted so that the vacuumed water will bypass the filter
and run to waste.
It is recommended that the pool be vacuumed
about once weekly, the exact schedule to be determined from the pool
Hair, lint, leaves and insects which enter the
pool and remain floating on the surface can be easily removed with
surface skimmers. There are two types of surface skimmers-hand and
automatic. The hand skimmer is simply a plastic screen or net
attached to a long pole and should be used to remove the larger
floating objects such as leaves and grass.
The automatic surface skimmer is a device
which is attached to the filtering system. During the filtering
process, part of the surface water is drawn through the skimmer and
into the filter, carrying with it dust, small insects, and other
fine debris before these can settle to the pool floor.
The pool should be skimmed frequently since
most dirt enters the water through the surface.
Bathers entering the pool frequently carry
silt, grass cuttings and the spores or seeds of the fungus infection
known as "athletes foot". The foot bath has been accepted
as the most effective means of keeping these foreign materials out
of the water.
When used properly, it is filled with a
solution containing from one to two ounces of granular calcium
hyochlorite for each gallon of water. All bathers entering or
leaving the pool should be required to place both feet into the
solution for a period of not less than fifteen seconds.
TEST KITS AND THEIR USE
The test kit is perhaps the most valuable aid
to the pool owner and enables him to keep his pool in proper
swimming condition. An adequate test kit is one which includes both
a chlorine and pH test.
Most test kits use the ortho tolidine test for
total available chlorine. This test produces a yellow color varying
in strength with the amount of chlorine present in the water. When
the color produced corresponds to a chlorine reading between 0.3 and
0.6 ppm, the bather is assured that the pool is safe for swimming.
Since chlorine dissipates rapidly in hot weather and under heavy
bathing loads it is wise to test frequently to assure a sufficient
chlorine residual. Just how frequently is best left to the
individual pool owners experience. A colorless reading means that
all of the chlorine has dissipated and it will be necessary to add
more. A reading greater than 0.6 ppm indicates the presence of an
excessive amount of chlorine and bathers should not be permitted to
enter the water until the chlorine had dissipated to a safe level.
Tests for chlorine should be made about thirty
minutes after it has been added to allow the material to dissolve
and mix throughout the water.
The phenol red method is the most common way
of testing for pH. In this test, the color changes from amber at low
pH to purple at high pH, each color between corresponds to a
different pH number. When the color produced corresponds to pH
readings between 7.2 and 7.8 the water will be in proper chemical
balance. PH tests should be made at least once daily and more
frequently during periods of adjustment. When adjusting the pH be
sure to allow enough time for the chemicals to dissolve and to mix
thoroughly throughout the water before testing.
WEIGHT AND VOLUME MEASUREMENT
One gallon weighs 8.3 pounds.
One cubic foot weighs 62.4 pounds.
One cubic foot of water contains 7.5 gallons.
ESTIMATING POOL CAPACITY
Rectangular pool: length x width x average
depth x 7.5 = gallons of water
Round pool: diameter x diameter x average
depth x 5.9 = gallons of water
Oval pool: length x width x average depth x
5.9 = gallons of water
HANDLING OF POOL CHEMICALS
- Most swimming pool chemicals are stable,
retaining their effectiveness and strength for a considerable
period of time when stored properly. Be sure to keep containers
covered and in a cool, dry place.
- Calcium hypochlorite, whether granular or
tablets, are concentrated chemicals and can be dangerous if not
handled properly. DO NOT MIX THEM WITH ANYTHING BUT WATER. Do
not let them come into contact with heat, acids, organic or
combustible materials such as kerosene, gasoline, oils, and
greases, paint products, beverages, tobacco, soap products,
cleaning rags and paper, because fire might result. Keep away
from steam pipes, stoves, heaters and strong sunlight.
- Use plastic, glass, china, or enamelware
scoops, measures and spoons…and be sure they are clean and
- Measure and add any pool chemicals
separately according to directions. Do not mix with one and
other before adding to pool.
- Most pool chemicals are harmful to shrubs,
grass and foliage in concentrated from. Keep pool chemicals away
from plant life near the pool.
- Hands should be clean and dry when
dispensing pool chemicals. Do not use gloves. Wash hands
thoroughly after treating pool.
- Keep pool chemicals and stock solutions
away from eyes. If they should touch the eyes, wash thoroughly
- Keep pool chemicals in original containers,
firmly closed when not in use, and out of the reach of children
- Read all labels carefully before using a
pool chemical for the first time, and always follow instructions
Information on this
page was adapted from "Swimming Pool Care &
Maintenance" - Rockwin Products Co. - and is intended as a
basic guideline only. Consult the instructions on your specific
brand of chemicals for proper use and safety instructions.