it sounds to me like your day time temp is in the 90's and night time is in the 80's. What u need is one side of the cage to be 92 - 94 and the other side 82 - 84. and there shouldnt be a night time drop in temp. u also should have 2 hides. one on the hot side and one on the cool side. U may have trouble heating a 40 g tall tank. I tried to get the right temp gradient in a tall 30 g tank and gave up after a couple days of trial runs. If i were u, ditch the aquarium even though it looks nice, and get a rubbermaid. Welcome to the site, there is loads of info on here. injoy.