Originally Posted by Jcarroll
Sally lightfoot crabs die naturally from growing. They shell only gets to be so big and they end up outgrowing it, but don't molt it. It's weird. They end up almost suffocating for lack of a better word in their own shell. It's nothing with your tank, it's just what happens to them. I had a fish store that didn't sell me one because she said the crab was almost at it's maximum size, and wouldn't live much longer.
ummm what? all crustacions molt. they will molt more as juveniles, but then it will slow down. they will continue to molt and grow their whole life, like a snake. these crabs can live a few years easily, they can get 6" at least and even have occasionally been known to catch small fish for a meal at that size.
your particular case, did it feel light when you picked up the supposed corpse? it could very well have been a molt, sometimes it is very tricky to tell. you may well see him in about 3 days.
is your tank new? did you ever dose it with copper? do you use tap water? what are your water parameters? sometimes if you buy a used tank from someone you can never be sure they did not dose with copper at one time or another.