ok 12/17/10 I bought a new aquarium heater for my 10 gallon so I put it on around 6 in the afternoon so its the next day and the temperature has dropped 7 degrees! it went from 77 to 70! I always turn my aquarium light off at 9:00 and the tank usally cools off because of the light not being on so I got a submersible tetra heater 10-30 gallons and it constantly turns off. like I counted how many seconds it was on it stays on from 40 to 61 seconds is that long enough to keep the temperature at a 76? or 77?