Dead algae in pool but water IN sand filter gross green


Apr 13, 2013
East Texas
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....

FC 17
CC .2
PH 7.8
CYA 35
TA 200
CH 200


Well-known member
Jun 22, 2013
East TN
I have same problem every year when opening too but never during the season. What I found was best to do with the filter is to mix some powdered chlorine (calcium hypochlorite or dichlor not trichlor, bleach not strong enough) in a bucket to where its a strong solution. Turn on the filter and pour the bucket in the skimmer along with the water flow. Then turn off the filter when you think the chlorine is in there and let it sit for awhile. Then backwash it. Snotty, bubbley looking grey matter will come out. May take more than once.