I use helix and VE thermostats for my tubs, with the probe taped to the flexwatt.... I have to have my Helix set at 108 to get a 90 deg reading on the substrate..... Where is your probe attached...? If i were using an aquariums to house my snakes, I would tape it to the bottom on the outside of tank and have the probe setting on top of the uth.... Your thermostat will more than likely read higher than the reading on the substrate..... I have never read that u should use a light in conjunction with a uth..... That is simply not true... But no one who houses a snake in a tank wants it to be dark, you all want to see your animals.... If this is the case just use an aquarium fixture with a fluorscent tube..... They give off very minimal heat....