I have a mesh safety cover and live in the Northeast, too. Since, with the warm, sunny weather, the risk of water temps approaching 50 (which would allow algae to grow) is going up, I opened up my corners yesterday, one at a time, (water is still clear ) and put some Polyquat algaecide in, then reclosed the corners, then I added some more in the skimmer openings. With only 2 anchors open at a time, there's no risk of anything harmful happening. Lenny's idea of using a submersible pump to move the water around is a good one - I may have to try to do that sometime.