HCA: Hermit Crab Association

We have 2 crabs about a month now. 20 gallon tank, sand and eco earth mix. Heating on the back of the tank; humidity is not between 75-80% and temp is 77-80. I had an issue with high humidity for about a week 95-99%. I have fresh water and salt water for them. Both waters have no choline. When I had the high humidity I did have an issue with white spots showing on the the tank glass (I wiped them off the glass). My crabs have both buried themselves and I haven’t seen them in about a week now. I’m worried about them. I smoothed the sand out a couple of nights and I don’t see any markings in the sand I can’t even see their entrance hole. I’m worried with the humidity being so high that there is mold in the substrate. What are the odds that both are molting right now. Do I go looking for them? Change the substrate??

Sounds like everything should be fine! High humidity is not a danger to hermit crabs, and try not to touch the sub as to avoid potentially collapsing any caves/tunnels they’ve formed. Just let them chill and be crabs!

I agree with the previous poster. Keep putting food out though. I find that my tat goes through cycles. There will be times when the crabs are all up and they're very active, and times when I hardly see anybody out for weeks at a time. They'll show up eventually

Thank you both!!

Sorry me again! So what happens if their cave collapses? Are they able to crawl out? Also, how would you add more substrate after you have the crabs in their home?

The white spots you see is surface mold, it will not be deeper in the substrate like a bacterial bloom. The white fuzzy is not harmful to a crab like a bacterial bloom.
If a tunnel or cave collapses and the crab is at a vulnerable point in the molting process, he can not dig out and will die. That said, just lightly smoothing the surface of the sand is unlikely to cause a collapse. Things like pulling items out of the sub or pushing items into the sub, moving the tank, or packing down the substrate could cause a collapse. You can safely add substrate while they are underground, just don't drop it in from a height or pack it down. Some people are cautious and only add an inch per day. How deep is your current substrate?

Ok thank you! Obviously nervous new crab owner here! The substrate is 4 inches now. I didn’t realize when I set it up that it should be 6 inches. I think I can see what looks like tunnels along the glass now.

It doesn't necessarily need to be 6 inches. It should be at least 2-3 times as deep as your largest crab. So if you have tiny crabs, 4 inches might be plenty! And if you have jumbo crabs, 6 inches might not be enough!