Swimming Pool Chemistry & General Operations

CHLORINE, ITS PURPOSE AND APPLICATION: 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 water.

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 your dealer. 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 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.


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 same range.

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.


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.


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 owners experience.


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.


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.


One gallon weighs 8.3 pounds.

One cubic foot weighs 62.4 pounds.

One cubic foot of water contains 7.5 gallons.


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


1) 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.

2) 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 steampipes, stoves, heaters and strong sunlight.

3) Use plastic, glass, china, or enamelware scoops, measures and spoons and be sure they are clean and dry.

4) Measure and add any pool chemicals separately according to directions. Do not mix with one and other before adding to pool.

5) Most pool chemicals are harmful to shrubs, grass and foliage in concentrated from. Keep pool chemicals away from plant life near the pool.

6) Hands should be clean and dry when dispensing pool chemicals. Do not use gloves. Wash hands thoroughly after treating pool.

7) Keep pool chemicals and stock solutions away from eyes. If they should touch the eyes, wash thoroughly with water.

8) Keep pool chemicals in original containers, firmly closed when not in use, and out of the reach of children or pets.

9) Read all labels carefully before using a pool chemical for the first time, and always follow instructions exactly.

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.

CHLORINE – 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.

Ph – 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.

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.

STABILIZER – 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.

REMEMBER – Good water chemistry can only be achieved when all four of these 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 !


ALGAE: Tiny plants which grow in the water and can discolor it.

ALGAECIDES: Chemicals which kill algae and prevent new algae growth.

BACTERIA: Microscopic organisms (germs) which can cause illness.

CHELATING AGENTS: Chemicals that combine with dissolved metals to prevent water discoloration.

CHLORAMINES: The combined form of chlorine after oxidation of impurities. Cause eye irritation and four chlorine-like odors. This form of chlorine is not an effective disinfectant.

CHLORINE: The most commonly used disinfecting agent for swimming pools because it is the best chemical material available.

CHLORINE DEMAND: The materials in the water which use up chlorine, such as bacteria, algae, dirt, leaves, grass clippings and swimmers wastes. The chlorine demand must be satisfied before a chlorine residual is available to disinfect the pool water.

CHLORINE RESIDUAL: The chlorine level in the water after the chlorine demand has been satisfied. The free chlorine residual is the true measure of potential chlorine disinfection.

CYANURIC ACID: (See stabilizer. Also called conditioner)

DPD: An indicator solution used to measure the free chlorine residual.

DRY ACID: (Sodium bisulfate) A granular material which is used to lower the pH or total alkalinity.

FREE CHLORINE: Hypochlorous acid or hypochlorite. This is the active chlorine that kills bacteria and algae and keeps your pool clear and clean.

HARDNESS: The amount of calcium or magnesium dissolved in the water. High levels contribute to scale deposits.

HYPOCHLOROUS ACID: The active form of chlorine in water. The material which performs the sanitizing and oxidizing. (free chlorine)

MURIATIC ACID: A liquid used for lowering pH or total alkalinity.

OTO: orthotolidine. And outdated indicator solution that was used to measure the total chlorine residual.

PH: A system for measuring the acidity/alkalinity of water. Readings above 7 are alkaline; readings below 7 are acidic.

Ppm: Parts per million, the standard measure of concentration in swimming pools. An example is one penny in $10,000.

PHENOL RED: The indicator solution which measures pH.

SHOCK TREATMENT: (See super-chlorination)

STABILIZER: (Cyanuric acid or conditioner) s-triazinetrione, also called Isocyanuric Acid. A chemical which helps prolong the useful life of chlorine in the water by slowing down chlorine decay due to sunlight.

SUPERCHLORINATION: (Shock treatment) The practice of adding 5-10 times the normal daily chlorine dose to destroy algae, or to prevent problems after heavy bather loads or severe rains.

TOTAL ALKALINITY: This helps the water resist changes in pH.

TOTAL CHLORINE: The sum of the amount of free chlorine and combined chlorine.

Information compiled from articles found on Poolandspa.com (www.poolandspa.com)

Leave a Reply

Your email address will not be published. Required fields are marked *


Enjoy this website? Please spread the word :)

Follow by Email