How Much Chlorine Should Be Added to a Pool?

The amount of chlorine a pool needs depends on a number of factors, starting with the volume of the pool. The short answer is add enough chlorine to maintain a free chlorine residual of 1.5 to 3.0 parts per million (ppm). The free chlorine residual is a measurement of the sanitizing form of chlorine. After you know the basic chlorine demand for your size pool, you can compensate for the other factors.

Using Water Volume as a Guideline

The first thing you need to know is how much water is in your pool. If you don't know this basic part of the equation, use the calculator in the Resource section to determine the volume of your pool.

Water weighs 8.34 lbs. per gallon, and free chlorine residual is measured in parts per million. This is a weight-to-weight measurement. For example, if you have a 20,000 gallon pool, you have 166,800 lbs. of water (20,000 X 8.34 = 166,800). A gallon of liquid pool chlorine contains about 1 lb. of pure chlorine. To determine how many parts per million 1 lb. of chlorine provides in a 20,000-gallon pool, divide 1,000,000 by the total pounds of water: 1,000,000/166,800 = 6 ppm. Therefore, to achieve a free chlorine level of 3.0 ppm in a 20,000 gallon pool, add 1/2 lb. of pure chlorine or 1/2 gallon of liquid pool chlorine.

Other Factors Affecting Free Chlorine Residual

The free chlorine residual is affected by bather load, debris blown in by the wind and carried in by bathers, splash out and refilling, circulation and filtration, temperature, sun exposure and the balance of other chemicals in the pool. Of course, these factors all vary with the season and use of your pool, as well as how often you perform routine maintenance procedures. These variables will always drive the chlorine demand up from the basis calculation.

Chemical Balance

Chlorine is most effective when the other chemicals are kept in balance. If you keep the pH level between 7.2 and 7.6, the total alkalinity between 80 and 100 ppm, the calcium hardness below 400 ppm and the total dissolved solids between 1,000 and 2,000 ppm, you will need less chlorine to provide the ideal range of 1.5 to 3.0 ppm.

The best way to keep the pool in balance is to test regularly with a good titration type test kit, such as a Taylor kit. Using a kit like this not only tells you what the chemical levels are, but you can also determine exactly how much of each chemical, including chlorine, you will need to add to balance the water under the particular factors affecting your pool.

References

• Online pool maintenance manual

Resources

• Pool water volume calculator
• Taylor test kits

[maryanne09]

on 10/18/2009 Great article on How Much Chlorine Should Be Added to a Pool?! 5*'s :)