lol, Carolyn. I really doubt we would have any problem with green stuff in the winter. Or perhaps you are thinking that the UV would kill microbes or such. Anyhooo, the large pump, the biofilter and the pressure filter with internal UV are all shut down and in the garage along with the freestanding 55W UV we got this summer. The circulating water seems to be keeping the water open a little longer and/or larger area on the surface. I think that is because Damien stuck each tube end into the rock to try to get circulation into the caves where the fish spend the winter. Seems like otherwise they would deplete the oxygen in there and just never wake up. We have had bad luck over wintering the larger fish. But it does come out somewhere at that end, so we are guessing the reduced ice mass is due to that. Plus the pump where the water is sucked in is right under a deicer so maybe for now the water is a tetch warmer, although this I doubt. I think it is just the water movement.
