To increase free chlorine (FC) in a 20,000-gallon pool by 2.0 ppm, how many ounces of calcium hypochlorite are needed?

To determine the amount of calcium hypochlorite needed to increase the free chlorine (FC) concentration by 2.0 parts per million (ppm) in a 20,000-gallon pool, it’s essential to understand the relationship between the volume of water, the desired concentration increase, and the characteristics of the chemical being used.

Calcium hypochlorite typically contains about 65% available chlorine. To effectively raise the FC by 2.0 ppm in a 20,000-gallon pool, you can calculate how many ounces of calcium hypochlorite are required based on the concentration you're attempting to achieve.

One ppm in a pool equates to 1 milligram per liter, and since there are approximately 3.785 liters in a gallon, raising the FC by 2.0 ppm in a 20,000-gallon pool means you need an increase of:

2.0 ppm x 20,000 gallons = 40,000 mg of free chlorine.

Convert this to ounces since the chemical is measured in ounces. There are roughly 1,000,000 milligrams in 1 ounce, so the requirement in ounces is:

40,000 mg ÷ (0.65 (available chlorine fraction