Shocking a pool converts chloramines to free chlorine, the form of chlorine required for proper sanitization of the pool. Chloramines form when chlorine binds to chemicals in suntan lotions, perspiration and cosmetics. They give the pool a strong chlorine odor but do not kill bacteria and algae.
Regular shocking is an essential part of a pool owner's weekly maintenance schedule during peak swimming season. Pools require shocking when algae is present, when the chlorine level drops to zero or when the free chlorine level increases to above 0.5..
Shocking a pool involves raising the free chlorine level to a point 10 times higher than normal, a level experts call break point chlorination, The process sometimes requires trial and error to determine the right amount of chemical needed to reach this point. Experts advise that pool owners repeat the shocking process until the free chlorine level is at or below 1.0 parts per million, the total chlorine level is less than 0.5 and the pool is free of algae.
When a pool undergoes heavy use, it sometimes requires more frequent shocking. Heavy rain or long periods of sun also increase the need to shock a pool. However, regular testing is the best indicator of when to shock a pool.