Right now I am using a store bought heating pad under one side of a 40 gallon tank. its a 3 setting pad in a fire resistant cover and I have the setting on low as I found when used on my own skin that the medium setting after some time became quite a bit hotter than on low. the temp on the warm side reads 73 degrees, i have a thermometer attached to the back of the glass so this would be the temp in the air) the temp on top of the substrate is about 76. Im wondering if I need a 2nd source of heat from above to make the temp a little warmer or if this is high enough for healthy digestion?