HCA: Hermit Crab Association

I recently got 4 crabs for my 30gal tank 2 are med and 2 are small. They were all fine at first, eating like crazy, climbing ect. Then three out of the 4 went under.(so I figured no big deal their molting) the larger one and one med one would come up at night and eat and check each other out, and th...

I'm also thinking of getting on but have noticed that my crabs like to climb BEHIND a climbing mat that I have put on the back wall of my tank and I'm worried about them getting burned.. any suggestions??

Im new to the whole hermit crab world and have a question on some wood that I found today while outside... it's from a Hickory tree.. the limbs would work perfectly in my tank.. but I want to make sure they're safe to use first.. I've looked around on different sites and can't find anything.. please...