The amount of chemical “residual” which must be present in pool water is expressed as so many parts of disinfectant per million parts of water, abbreviated “ppm.” The same quantitative measure us used to express the amount of any other chemical added or present in the water.
Chlorine is the most widely used and accepted disinfectant for swimming pools. When chlorine is used as a disinfectant, at least 0.6 ppm and preferably 1.0 ppm of “free residual chlorine” MUST at all times be present in pool water to kill bacteria and algae and maintain the water’s purity. Critical though this “residual” is for pool purity, it is a very small amount of chemical. Less than one drop of chlorine in every 1,000,000 drops of pool water is enough to disinfect the pool, providing the chemical is 100% active.
Here is a list of the most common factors affecting the in-pool longevity of chlorine.
1) BATHING LOAD – The number of swimmers who use your pool. The greater the number of swimmers, the more disinfectant is used up.
2) SUNLIGHT – The greater the sun’s intensity, the faster the dissipation of disinfectant “residual” unless the pool is stabilized.
3) WATER TEMPERATURE – The warmer the pool’s water, the shorter the life of chlorine. This process is greatly accelerated when the water temperature exceeds 85 degrees.
4) WINDS AND RAIN – Carry dust, bacteria, algae spores and other debris into the pool, over working the chemical disinfectants and reducing their ability to sanitize.
5) pH BALANCE – As the pH of the pool water rises, disinfectant action slows down. More disinfectant must then be added to maintain the proper “residual.”
To maintain your pool’s bacteria killing residual, disinfectant chemicals may be added by hand or by a chemical feeder. Feeders may be adjusted to increase or decrease the feed rates of disinfectants, depending upon the chemical demand of your particular pool.
Granular disinfectants are simply sprinkled into the pool water. Begin at the deep end. Move completely around the pool, distributing it evenly throughout the pool. Some granular disinfectants must be pre-dissolved before adding them to the pool and may cause the water to become cloudy.