How would I do this? I have mine set up (kind with the knob at the top to change temp, sits in the water). but it is set to 76 and the water is definately much coler than room temp! The heater gets really warn with the light on for a few minutes.. and then turns off but the water is still frigid. Fish aren't happy with all the temp changes. It was working until I emptied my substrate out today and set the therm. up again