HCA: Hermit Crab Association

Hello! I am new to owning hermit crabs. I went on vacation to Galveston with my family about three weeks ago and we saw the awful enclosure they were being kept in and decided to try to take some home to give them a better life. I did a lot of research including using this website and watching videos from hermit owners online.

Some info on my equipment - I have a 20 gal tank for three crabs and currently it is about 2-3 inches deep inside, I plan on buying more sand pretty soon. The sand is hermit headquarters brand. I also mixed some of the eco earth coconut fiber with it. I also got a large heating pad that fits onto the entire length of the back wall of the tank. The temperature averages around 73 degrees inside so I ordered another pad to make it warmer. The food I give them is from the Etsy store southoftheocean. I try to spray their tank with saltwater I made with a gallon of distilled water, about 4 drops of API’s tap water conditioner, and instant ocean salt, at least twice a day. I also have two plastic things inside for them to submerge in, one containing the freshwater I made and one containing the saltwater I made. If there are any questions please let me know!!

About 2 days ago, I noticed the most active crab, King, was hanging out of his shell. This really worried me as I knew it was a sign of either death or him trying to surface molt. I read somewhere on here of someone’s crab doing the same thing and they took it and put it in its own small tank with a small amount of water for hydration and their crab ended up being alive and just molting. My mother in law and I put on some gloves and did the same. However, I went to check on him and he is starting to produce a light fishy smell. I know this is a sign of death, but I have also read this is a sign of molting as well. I was wondering what exactly should I do? Is he dead? If so, can anyone give me any info on how he might’ve died and what to do to improve the tank? Because he was the most active of the three, I am very worried that my other two crabs might end up like him. Thank you!!!

Welcome to crabbing and to the site!
If you pick up the crab by the shell, does he stay in or fall out?
What is your humidity reading?
If you are wanting to be more thrifty, play sand is much cheaper than the Hermit Headquarters sand. Your substrate should be at least 2-3 times as deep as your largest crab, and moistened to sand castle consistency so that it holds its shape.
What is your humidity reading? That is important, as crabs have modified gills and need high humidity to breathe.
If you are misting the tank, don't use salt water, as the salt will build up over time in the substrate after the water evaporates.
HCA recommends using tap water treated with a dechlorinator that removes everything including heavy metals (SeaChem Prime is a commonly used brand) so that they get ground minerals - and then a marine salt (Instant Ocean is a commonly used brand) for their ocean minerals. Read the 'water' care sheet for full details.
If you are going to isolate a crab, you have to be sure that the temp and humidity are both good - some people will use a margarine container or similar with holes cut in it, in the main tank so you know the conditions are good.
If you haven't looked at the care sheets yet, start with the 'basics' one.