Don't use a heat mat. It barely heats the air in the tank, just the glass which if it's on the bottom the frog can come into contact with it and dehydrate/burn. I was using a mini size matt on the bottom until I realized it was heating the bottom glass to upwards of 100°f and the air/top of substrate was still room temp. I switched it out to one of those blue "moonlight" bulbs which has worked for me so far, barely any light really, but a low watt ceramic heater (w/ a thermostat maybe) sounds best.