I had mentioned cooling my home to 77 because I found it surprising that the water temps rose to 81 with the air temps at 77, I expected it to be closer to 1 or two degrees. More this is across the tanks , a 55 gallon, 75 gallon, and a 5 gallon we have fry in. Mine is the 75. I haven't gone into detail on the other two because they are mollies and platies which my gf says handle temps better. Mostly this has been a bit of a surprise. We are along the coast of Virginia where we have weeks in the 70s in the winter and then weeks of 40s with some extremes beyond that but short lived. The tanks never got above 79 in that time. Nights are still cool though. Today in the spring it topped at 75 I think in the house with the windows open but the tanks still were at 80 degrees. The only difference between now and two months ago is the nights then cooled down much more. I have propped the lid open with no effect and have great surface disruption with my canister output going across the length plus a 9 inch bubble bar, 6 inch bubble disk, and a hang on back filter. Trying not to go to extremes with a chiller if I don't need to but will if I need to. Is it common to have a 3 to 4 degree difference between the air and tank?