I recently moved my 10 gal. tank from my kitchen to my living room. In the process my heater broke. I have an extra from a 55 gal. I put it in last night and set it to 80*F and figured the thermostat would take care of the rest. This morning temp was at 86*f. I turned the heater down to 75 and will check it when I go home for lunch. I figure if I monitor it closely there will be no problems, but It is pretty big and I could be overlooking some problem that might arrise. I won't be able to get a new heater till friday, someone tell me I wont cook my fish during that time.........