I use Ultratherm heat mats. They have a fairly low wattage, not sure on specifics as sizes might have different wattage. The UTH should cover 1/3 of the tub, if I remember that correctly (it's 2:30 AM, my apologies). The UTH's are put on the outside of the vivs/tubs and on the bottom. Not sure what kind of thermostat these are but your best bet is a Herpstat by Spyder Robotics. Fantastic thermostat, you'll definitely need one. The probe for the thermostat also goes in between the bottom of the viv/tub and the UTH. It's recommended to use aluminum tape to hold the UTH against the tub. Works well and doesn't deform. Some use hides some people don't.