I forgot to ask in my last reply: Given the the temperature of the tank floor is what matters, should I set my thermostat to the temperature I want it to be so that the tank floor is 90 degrees, or should I set my thermostat above that temperature so the substrate surface reaches the temps I want? The latter seems dangerous for the reason you stated, they could bury and get burned, but the former seems to not keep them warm enough. Which would you recommend?