HCA: Hermit Crab Association

I'm moving from a 10 gallon tank to a 20 gallon long and have some questions I hope some of you can answer. I want to put a background on the new tank because I didn't have one on my old one. How do you put a background on AND have a under tank heater? I noticed that some put the under tank heater on the left or right side of the tank walls instead of the back, but would that keep the temperature up and the crabs warm? Any under tank heater bran recommendations fora 20 gallon long? Could I put the background on the back of the tank and then put the under tank heater on top of the background, or would that mess up adhesive and cause a mess? Is there a way to take off the 10-20 gallon heater I have on the 10 gallon and reuse it on the 20 gallon long? I understand the adhesive might not stick again so is there some type of adhesive spray that withstands heat that I could spray on it to make it sticky again? Also does an enclosed 10 gallon create more humidity than a 20 gallon long because there is less space? My humidity in the 10 gallon was always in the 80-90s, hoping that the 20 gallon long brings it down a little. Sorry to seem overwhelming!

With regards to your question about putting the heating pad on the sides as opposed to underneath, as far as I am concerned, it does keep the temperature warm for the crabs. I have a side mounted heat pad and served me well for the past 8 or so years keeping my two purple pinchers successfully. The side pads are placed about 3 inches or so above the substrate line, and far away from any possible contact from any ornaments or climbing areas to keep the crabs from touching the heated glass areas.

The reason that I don't personally recommend placing heating pads underneath is that you will risk literally cooking a molting/sleeping hermit. This happened to me once when I unearthed a dead (apparently cooked) hermit about ten years or so ago (I posted this story a long time ago - probably deleted now, but a really old HCA post). Since then, I have used side mounted or top mounted heating for the tanks. I think the same applies to pet herps (lizards, snakes, or tortoises) as well to avoid burnt bellies, I believe.

Ideally, heating should be from the top mounted source (ex. ceramic heat emitter or heat bulb) and that the hermit crabs will not be able to climb to get to them or come in contact with them perhaps via a screen or just keeping any climbing ornaments far below from the top mounted heat source. The substrate is essentially unheated (you know, kinda like a hot day in the beach, when you bury your feet in sand to cool off a bit - that's one way of land hermits cool off to avoid the heat of the tropical noontime sun, buried in substrate).

Once I got a used 20 gallon tank with a under tank heat pad permanently stuck underneath it that I couldn't remove without, I thought, breaking the bottom glass, so instead of removing or using it, I just made sure that the power cable was rolled up, unused, and inaccessible (in hindsight, maybe I could have cut the power cord so I didn't accidentally plug it in) and bought a brand-new non-adhesive heat pad that I mounted to the side to be used as the new heating element.

I don't know about reusing a pad that was self-adhesive. I have no advice to give about reusing self-adhesive pads with regards to using adhesive sprays. sorry. But I just wanted to let you know that you can heat a tank with side mounted pads.