I use 1-2 sheets of newspaper and a small amount of aspen, and I only have to set the thermostat at 95 to generate a 93 temp. I notice I get hot spots if I don't fluff the aspen, but otherwise have no problems. Something's not right there. I agree with April you don't need such a wide difference in temps. Stick with a 1 degree difference and set the temp where you want it to stay.

Is this a rack or just a single tub? Is there any space between the floor, heat mat and the tub?