The tank must be in a room with poor insulation. It feels quite cool at nighttime when I feed the fish. The heater is set for 81. Mainly because in the summer I couldn't get it lower. So yesterday morning the temp was 82 which is typical. Last afternoon it went down to 81 and last night it was 80. Now it's 80.8. Is this big temperature swiching thing a problem? Is the heater doing okay, because it's set for 81 and it's below that. anyone else had problems with tanks due to winter?