My pool AG 27 ft with sand filter is sparkling clear. But after running filter dead algae remain on bottom in clumps. I have tried vacuuming and vacuuming to waste but that does not solve problem. I changed sand, even changed to fine Zeosand but no dice. The algae seem to puff into smoke when I vacuum, and if you step on the algae it disappears. I tried experiment by vacuum to waste, getting pool to look clear, then ran a pump in pool circulating water but bypassing filter completely by keeping it shut off. After 30 minutes I shut off pump and again all the dead algae appeared on bottom. I also tried flocculent and skimmer socks ; nothing works. I have had this problem for seven years now and am about to give up and deal with it, but any suggestions?