im using a fairly decent hygrometer, it has these neat probe looking things that i hav carefully hidden around the tank to take multiple readings of cool side, cool hide, hot side, hot hide, and middle. i even hav one to measure the humidity of the room the tank is in, so i know if there is a sudden drop that might influence anything. this applies to temperature as well. i know that sounds like a lot of wires and testing nodes, but i assure you they are all VERY small and all run from outside the tank, under the substrate, and up into the tank itself, no thicker than a fishing line. could it be soething other than humidity?