Something that many people don't understand about those tabs is that they contain CYA. Although all outdoor pools need some CYA, continuous use of the tabs over a long period of time cause CYA levels to get too high. Once it is high, then you have to run higher than normal chlorine levels or you end up with algae problems. Most people don't understand the connection between CYA and chlorine. Take a look at the Best Guess Chlorine Chart in my signature below for more about that.