I use the same thing, it's under my tank and get's VERY hot. I got a plug in dimmer from Home Depot (^^like she said) for $10.00. I also measure the temps using a temp gun. My dimmer is set below halfway...that's how hot they get. Home Depot should have temp guns also (you may have to explain to the employees what they are before you get the isle they are in), but if not the PE-2 which is awesome is on sale on tempguns.com for $35.00. Depending on how hot or cold your house is, you may have to adjust the dimmer like 2-3 times a day, and take temps with the gun. Hope this helps! Good luck