The tank used to be sand on one side and coconut fiber substrate on the other, but I just replaced it with about a 50/50 mixture of the two. It is about 1 1/2 inch deep in a 10 gallon tank. It is also damp and fluffy so I imagine it would be comfortable for a crab to dig down into and molt. I have this heating mat directly under it, and it has worked well to keep the tank warm without overheating. It is at 81° F and 81% humidity right now.

I have one crab and I mostly feed it this, or sometimes scrambled eggs or whatever fruits and vegetables I have in my kitchen. I fed him boiled carrots and peach mash today. The illness he had before could very well be from a lack of nutrition, so I will start feeding him more fresh foods more often, rather than relying on the hermit crab meal as a food staple.

Luckily there were no mites when I cleaned the tank out yesterday. Thank you for the link, the little white bugs I saw must have been some sort of food mite larvae. I will refer to that if I ever have a problem with them again. I successfully terminated them when I lost my other crabs (to who knows what, if the mites are harmless) and have not seen any in the crabitat in over a year. I'm glad that's something I don't have to worry about now.

Again, thanks for the help! I will update my main post with pictures.