The ideal concentration of chlorine in a swimming pool is 1 to 2 parts per million (ppm). It is safe to swim in pools with concentrations of up to 3 ppm, but concentrations greater than 2 ppm cause eyes to burn. Concentrations of less than 1 ppm allow slime to move in.
Since chlorine concentrations of 3 ppm or less dissipate in reaction to bacteria and the sun at a rate of about 15% of the amount present per day, it is normal practice to add small amounts of chlorine every day to maintain a concentration within this 1 to 2 ppm ideal. However, occasionally pools need to be given a very high dose of chlorine to clean out the pumps and filters as well as the pool itself. This is called "shocking" the pool, and the high chlorine concentration drops fast and is down to 3 ppm after about two hours.
Suppose after "shocking" a pool, we add 1 ppm a day. Assume that the concentration begins at 3 ppm. What happens to the concentration of chlorine? At what concentration, if any, does the chlorine stabilize?
Suppose we add 0.1 ppm per day instead. What happens to the concentration of chlorine?
Can you find an amount to add that will keep the concentration at the original 3 ppm level?
Can you find an amount to add that allows the concentration to stabilize at 1.5 ppm?
Write a brief paragraph on maintaining an appropriate level of chlorine in a pool for an owners manual.