Every sanitizer has two key functions, to sanitize (kill bacteria and all living organisms) and also oxidize (destroy contaminants and waste). The most popular pool and spa sanitizer is chlorine. Chlorine is also classified as a disinfectant, meaning that it is capable of killing bacteria, algae and other organic material instantly. All chlorine does the same thing when it is added to the water, regardless of the type of chlorine added. It forms free available chlorine. Free chlorine is the form of chlorine that kills bacteria, algae and disease-causing organisms. It is the attack dog that guards your pool against microbiotic intruders. (In general, you wouldn’t want a dog in the pool, but this is an exception.)

You must maintain free chlorine at a sufficient level to disinfect potential contaminants on contact. The more chlorine in the water, the more it can sanitize and oxidize the water. (Remember that sanitizing and oxidizing are the processes that chlorine uses to keep the water clear and clean.) However, if the free chlorine level gets too high, it can make the water uncomfortable for swimmers. The trick is to keep the free chlorine level in the ideal range. In a swimming pool, keep free chlorine at a minimum of 1 ppm (parts per million) and a maximum of 10 ppm, with an ideal concentration of 1 to 3 ppm.

In spas the level needs to be maintained at a slightly higher level due to the smaller volume and higher temperature. The minimum level should be 2 ppm in a spa, again no higher than 10 ppm, and ideally 3 to 5 ppm.

Adjusting Chlorine

You want the Chlorine level between 2 and 4 ppm.

% is available chlorine in compound, 35% = .35

Raise: ozs of chlorine = gals x ppm x .000128 / %

Lower: ozs of sodium bisulfate = gals x ppm x .00034
Lower: ozs of Muriatic acid 31% = gals x ppm x .000256

To raise chlorine in 9,500 gallons of water.

1 ppm with 2 oz's of chlorine
2 ppm with 4 oz's of chlorine
3 ppm with 6 oz's of chlorine
4 ppm with 8 oz's of chlorine