I think I've killed my heater. The lowest temperature it seems to be able to maintain is 85-90 degrees(F). It's one of those submersible heaters. Is there any way to recalibrate it or will it need replacing before I actually need a heater? I've got another heater running in my fish tank...I got the two of them simultaneously because I had two tanks at the time. I'm testing this one because I want to get another tank going. Anyway, maybe this heater wasn't allowed to sit unplugged for 15 minutes in the water before it was removed?