i really do question the value of pucks myself..i always have one in the system, but i think it is only really effective as a chlorinator when conditions are optimum (pool is not really hot, no sun, no wind that all thieves away chlorine) case in point..i put in bleach on sunday...it was good until yesterday and we've had 3 very hot days in a row..yesterday..0 level on the taylor test kit for chlorine..even with a puck in the skimmer and good circulation..one more reason i'm converting to a chlorine generator..just pissing away money on pucks..