My sand filter was a 300# version (Hayward 3.1 ft^2), coupled with the 2 speed whisperflo motor. At high speed I could see dirt/algae blown back into the pool when vacuuming. At low speed, it was grossly underfiltered (@ 24 hr/day). I added a bit of DE, which helped slightly but not enough. The big problem with my pool is the undersized skimmer and drain lines, but I'm not willing to rip up the deck.
I should also mention that the whisperflo is 1.65 SF HP.
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