I'm currently using a 20L critter tank, between 1/4 and 1/2 inch of eco earth and the "medium" 8 watt exo terra rainforest UTH. I have a thermostat, but it has nothing to do with this. I have the accu-rite like everybody else, and I have the probe stuck on the glass directly over the heater. The probe hasn't read higher than 88 degrees since it's been hooked up. SO I remove the thermostat and plug the heater directly into that wall (never fear, no snake in it yet) and leave it over night. I get up this morning (6-7 hours later) and it's reading 85 degrees. Obviously I need more heat, but is this a normal range of operation for this particular heater? anyone else using it have any issues? Maybe I should buy another higher wattage heater and convert my hot side to my cool side? Do these things really take days to reach actual heat? I don't know. Any thoughts?