Topher, are u using a IR light? or any other light source? if so git ride of it, u will gain Humidity. i recently had my setup using a combo of UTH and one IR light. i was using towels as substrate and while we had a humid summer it was fine. recently i switched to aspen and i noticed at least a 10 - 12 % drop in humitidy which i tried to fight while i still used the IR light. I lost the battle and ditched the light and added another UTH in the center of my 45g aquarium. everything is running smooth again.