So the temp in one of my 10 gal tanks has started to swing from 72 degrees in the morning to 88 degrees in the afternoon. I'm at a loss here. Anybody have any recommendations? I have a heater btw, and it doesn't help...I've tryed like 4 different heaters. I've also tried different thermometers.

What's causing the swing? Is it the lights? Does the room temp vary that much? Is it by a heater vent or a window?

I'd guess the heat from the lights is building up. Maybe you could time out the lights for a couple of hours during the day. Otherwise, it sounds like you might need to have some sort of controller to turn the lights off, heater off, and a fan on.

I'm with mskohl. What does the temp get down to in the middle of the night? Get a bigger heater if it is getting really cold at night... and a small fan for the day will help.