HCA: Hermit Crab Association

I have a hermit crab that I bought about a year ago. I have had him in a 75 gallon tank with a few other hermit crabs. The habitat has 7-8inches of sand and coconut substrate, with two large/deep pools one salt water the other fresh. I use repti safe for the water and FMR soaking salt. The habitat has hanging coconuts with bridges for them to climb and play on. The ground has a few places to hid along with lots of vegetation. We keep a mix of food available for them, we add freeze dried fruits along with a sprinkle of FAUNTA hermit crab meal that supports growth, a sprinkle of JURASSIDIET hermit crab formula that supports immune systems, and the THRIVE hermit crab variety. We keep their tank clean and ensure they have a large variety of shells to choose from. This particular crab we bought about a year ago, and he has seemed to adapt to the new environment very well, however he was always scared of our hands and retracted into his shell. For a good portion of this year he stayed burrowed in the sand and would have short periods where he would come up for food and water. A little over a week ago I noticed him sitting in the hanging coconut for several days, then he moved down to the sand where it had been dug out by the glass, he sat there for about two days then moved back up to the regular level and was eating but not moving very much. I worried that he had been sick possibly and isolated him in a smaller tank. The smaller tank had a soaking pool, vegetation, a few shells, sponge, fresh food, heater and I misted it with water often. The temperature has stayed between 75-81. The first day or two he didn’t move very much but soaked in the water. Last night he was moving around the tank and eating. I thought he was feeling better. I woke up this morning and found him completely out of his shell soaking in the salt water. His shell sat in the corner. He has never done this before. I know this is not a good sign. I read that boiling shells in salt water would make them more attractive, so I grabbed a few shells he might like and boiled them in salt water then added to the tank. I also sprayed the tank and he barley moved. Normally he would have retracted into his shell and without a shell on he didn’t move a bit with water spraying in the tank. Although the has stayed burrowed for a good portion of the time we’ve had him we are unsure if he has molted and he has not changed shells. Our other crabs are in the larger tank healthy and running around playing and of course causing chaos as usual. (They will dig under the little decorations and such and knock over everything pull sponges out of the bowl etc. they seem to enjoy making a mess) please provide any insight as to what could possibly be wrong or if there is anything further we can do? He was very very dark when we got him which may indicate he is much older but we are unsure. He is a larger crab but not the largest of our bunch. Thank you for all advice!

If you haven't already, read through the 'naked crab' care sheet. The priority will be getting him back into a shell. Once you do, try feeding high energy foods like honey and peanut butter.

https://www.hermitcrabassociation.com/p ... 7&t=122302

You are correct, unfortunately, that it does not sound good for your crab. It is hard to know exactly why a crab does not thrive sometimes, as we don't know what they went through before we got them, and there is no way to run diagnostics.

While I doubt it is what is causing the problems with your crab, there are a few things that you may consider changing.
Your dechlorinator and salt may not provide everything needed for long term health.

https://www.hermitcrabassociation.com/p ... 27&t=92553

You don't need sponges in the water, all they do is harbor bacteria.

Do you have a hygrometer to measure your humidity? You may not need to mist much, if at all, if your humidity is good. Misting can sometimes cause problems if you add too much water into the tank and over saturate the substrate causing a flood.

I'm not familiar with your brands of food, but some people limit commercial foods due to additives. Here is our care sheet about commercial foods.

https://www.hermitcrabassociation.com/p ... 25&t=92555

Update: 1/17/24
After a few weeks of keeping the crab isolated, with fresh food, proper humidity, temperature, several inches of sand, several shells, plants, salt water, and fresh water pools, our little guy unfortunately didn’t make it. At one point he had gone back into his shell and started acting normal but then de- shelled again and spent about a week switching between water baths before he passed. I didn’t see any signs of mites or any obvious evidence as to why he died. My other crabs are doing well with no signs of sickness. It’s unfortunate that we lost him, however it helps to know he was in a very good habitat for the last year of his life in our home. I’m not sure how old he was but that’s the only reason I can think of for his death. Thank you for the advice, I appreciate it.