I set up a new 10 gallon tank and am doing a fishless cycle and letting some of my plants grow. I'm trying to get the temp dialed in, but this heater is just killing me. It's been keeping the aquarium around 82 and I've turned it down incrementally over the past few days, but it seems to just stay on. Do you think the thermostat is broken. Should I just give up on it and return it? Any recommendations on a better unit?