I have a Stealth heater on my 20 long, can't remember the watts but it's whatever is rated+ for the tank size....I was doing a water change tonite and did not turn everything off :headshake2:; only the filter - the water level got low and the heater started smoking. There is a little algae on it and I am thinking/hoping that is what was smoking - but do you think my heater is fried?!?!!?!? 