Above Ground Pool Chemical Basics

Above Ground Pool Chemical Basics



For sterilization of pool water chlorine is the most widely accepted and used chemical. It is an efficient bactericide as well as good algaecide when used properly. The amount of chlorine required to maintain a pool in a safe sterilized condition will vary depending upon several factors such as water temperature, extent to which the pool is used, degree or airborne contamination, sunlight exposure, and balance of other chemicals and minerals present in the water.


It is a good practice to maintain a free chlorine residual of between 0.3 and 0.6 ppm (parts per million) in the water at all times. This is based upon the use of chlorine without any stabilizing agent, such as cyanuric acid. If a stabilizer is used, the chlorine residual should be increased to at least 1.0 ppm.


Chorine plays another important role in addition to its sterilizing action. During the process of use of a pool there is an accumulation of various nitrogen containing organic compounds in the water. These nitrogen compounds tend to reduce the effectiveness of chlorine as a germicide. However, when chlorine is added in greater strength it will literally burn these undesirable materials rendering them inactive. Because of this it is important that a shock dosage of chlorine, 5 to 10 times the normal dosage, be added once every few weeks when the pool is not in use to burn out the nitrogen materials. This is referred to as Shock Treatment or Break Point Chlorination.

Chlorine Residual (free available) is the reserve amount of active chlorine present in the water available to immediately act upon bacteria or algae contamination as it may occur. This residual should be tested for daily, preferably in the morning before the pool is in use. The chlorine residual test is made with your water test kit. Two types of test kits are generally accepted in the swimming pool industry, OTO and DPD. OTO

  1. (orthotolidine) upon the addition of a few drops of OTO to a sample of pool water, a yellow color will develop in the sample if there is any chlorine present. The amount of chlorine is indicated by the intensity of the yellow and is determined by comparison with calibrated color standards which are a permanent part of the test kit. DPD (Diethyl-p-phenylene diamine) with this type of test kit, a DPD chlorine tablet is added to a sample of pool water, the amount of “free” chlorine is indicated by comparison of the resultant color to the color chart provided with the kit. To be assured of safe water, the chlorine residual should be kept between 0.3 and 0.6 ppm (parts per million). If a chlorine stabilizer such as cyanuric acid is used, the residual should be increased to at least 1.0 ppm.


  1. pH. The balance between acidity and alkalinity is referred to as pH. It is represented by numerical values ranging from 1.0 to 14.0. A value of 7.0 indicates a neutral condition, neither acid nor alkaline. Values below 7 represent an acid condition increasing in intensity as the numerical value decreases. Alkaline conditions are represented by values above 7.0 increasing in strength as the numbers become greater. The ideal pH for pool water is generally between 7.2 and 7.6.


  1. Balancing the pH. If the pH deviates too far from the normal it should be adjusted.


  1. Low pH. When the pH drops below 7.2 it should be adjusted upward by the addition of small quantities of soda ash. Too low a pH causes skin and eye irritation and will accelerate corrosion of pool equipment.


  1. High pH. If the pH rises above 7.6 pool acid, either the liquid or the dry form should be added to the water. Whenever any acid is introduced into the pool, it should be diluted and thoroughly mixed throughout the pool, to prevent corrosion. A high pH reduces the effectiveness of chlorine as a germicide and an algaecide. This condition also causes eye irritation.

Above Ground Pool Chemical Basics

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