I am not sure if this was once posted in some shape form or fashion. I am lucky to know how to post on here. Anyway I have a 55-60 glass terrarium ( I think) it's fairly large. (46L by 17 H, and 17w.) I was just reading about surface temp vs. ambient temps. My temps in tank according to the acu-rite digital thermometer/ humidity is 84 on the hot side and 75ish-80 on the cool. When I say 84ish on the hot side I am talking about the temp that is outside of the basking area. If I move it closer to the basking area it gets in the 90's. What I was wondering do I need a uth?, and if so what uth should I get? Couple of problems with the bottom of the tank. One; there is a double pane of glass. When I bought the tank it had a huge crack. So I went to the glass store, and had them cut me a 1/8" thick piece of glass. I never removed the old glass; I just put a bead of silicone around the edge, and placed the new glass on top. It's just about a permafix because the glass was a snug fit to begin with; then the silicone. Two. Substrate; I have repti-bark covering the floor of the tank. I think I have about 1 1/2" to 2" of bark on the bottom. Any idea as to where I should go with this? Oh one thing I did forget about the bottom of the tank there's about an 1/8" bead of silicone. So there's an air pocket between the glasses. I am assuming in total from the bottom of the old glass to the top of the new it's about 3/16" thick. What is your suggestions?