With UTH you have to keep the substrate very thin. Newsprint or paper towels are good for that. When I had my 20gal I had to use Eco Earth for humidity. I made sure to keep the substrate thin, especially in the hides. Because in order for the substrate to get to the 88/90 whatever hotspot you want you have to crank the heat up. Then if they move the substrate they could be sitting on the glass that is hotter than the intended temperature. By keeping it thin you prevent that from happening because you don't have to turn it up like that.