Swimming Pool Chemistry and General Operations


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.

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