Chlorine disinfects pool water by killing harmful micro-organisms such as algae, bacteria, viruses and fungi. Chlorine levels can rise and fall dramatically based on factors such as water temperature, sunlight exposure, bather load and the amount of contaminants entering the pool from the air. The chlorine level, type of chlorine and the volume of water in a pool determine the amount of chlorine needed per dose to maintain optimum chlorination.
Calculate the amount of water in the pool by measuring the width, length and average depth of the pool. Determine the average depth by adding the depth of the deep end and the shallow end and divide by two.
Multiply the length, width and average depth and multiply that product by 7.5 for a rectangular or square pool. Multiply the width, length and average depth and multiply that by 5.9 for a circular or oval pool.
Use a chlorine test kit according to package directions. Kits are available that use paper test strips or liquid drops that are added to a measured amount of pool water.
Read the dosage rate on the chlorine container to determine the amount of chlorine needed to raise the chlorine level by 1 part per million (ppm). The dosage rate is often 10,000 or 15,000 gallons.
Divide the amount of water in the pool by the dosage rate to determine the multiplier for the chlorine dose. For example, if the volume of water in the pool is 23,000 gallons, and if the dosage rate is per 10,000 gallons, 23,000 divided by 10,000 is 2.3.
Multiply the amount of chlorine needed to raise the chlorine level 1 ppm by the result of dividing the gallons by the dosage rate. For example, in the sample above, 2.3 times the amount of chlorine needed in gallons or pounds that is printed on the chlorine product container. If the container states that the amount of chlorine needed to raise the chlorine level 1 ppm is 1 lb., multiply 1 times 2.3 lbs. of chlorine would be required to raise the chlorine 1 ppm for the volume of water in the pool. If the test strip shows that the chlorine needs to be raised 2 ppm, multiply the result by two.
Use this simplified equation: The total amount of chemical to add equals the actual amount of pool volume in gallons divided by the gallons from the product label times the amount from product label.