I have a 75g tank, 35 gallon sump, and a 300w Hagen heater in the sump.
I currently don't have my lights set up yet, the room is quite cool, and the tank is currently cycling.
My problem is that even though I have my heater set close to 90 (I want a constant 80 if possible), the temp of my new tank fluctuates between 76-78. The heater is never on for more than 30 sec. It has been like this for about 4 days (since putting the heater in there).
Do you think my heater is defective?