Not sure where my bloom came from - taken everything out of the pool and never let the FC get below 2. Had husband take lid off sand filter tonight and the water in there is gross green. I've had it at 17ppm for 24 hours and the stuff in the pool is dead. Shouldn't the stuff in the sand filter be, too?? Always had a suspicion that it doesn't filter properly but how can algae be still green in a black sand filter with 17ppm chlorinated water running thru it? Had this happen at beginning of season, too. Sand was only a couple of months old but that rinse there were chunks of green algae in it. Each time I backwash I rinse and then pump to waste. Did that right before we opened it tonight....