Hey I use Play Sand with a heating pad underneath. I mixed my sand up really good with some water. (I hear bottled water is ok?) A few days later it was very very dry already. Is this due to my light, the heating pad underneath, my lid, how much sand I used? I have a 20g tank with the fishtank lid on it, plastic with a fold open flap and the light built in on top. My sand is 6 inches deep, my humidity and temperature are always good. I don't understand how it dries out so quickly. If I spray the sand with a spray bottle then the humidity becomes too high... Any suggestions?