He is in a 40 gallon breeder, glass tank. Screen lid (covered with aluminum tape except where the CHE is), the glass is covered on the outside (3 sides) with foam board insulation. I also have the CHE on an adjustable zoomed lamp stand. dangling three inches, got it. This would be to keep his ambient temperatures right so his cool end is about 80. Would it make more sense to put the probe on the cool end? his UTH is already on a thermostat so his warm hide is 90. I just realized I didn't mention his UTH in my original post