So I recently completed my "tortarium" with both a 100w light fixture and an under tank heating pad. Both came with the tank from the previous owner who used the set up for a snake. As I have been observing our new tortoise and really checking the heat situation, I have decided just to unplug the heating pad and figure out enough insulation and overhead heat to keep the tank warm enough. I am concerned that instincts may direct the little guy to burrow to get cool but the deeper he gets the hotter it gets! Does that make sense?