What type of lights are you running? Do you even really need the heater? With the proper lighting (pretty much any for that matter) you shouldn't have to run a heater at all. Our 125 is on VHO's, our 10 nano is PC and our 20g QT is just a plain NO and the temp always stays relatively steady at about 78F. You might just try taking the heater out altogether and monitor the temp (day and night) to see how it goes.