I bought some new crabs at the pet store, now my crabs are all dying!! 2 disappeared, not in substrate molting, one is missing all his legs and claws, I have to hand feed him, now my biggest baby is dead! He was very lethargic, I thought he was molting, but he started streaking and I spent alot of time putting him back into his shells, I bought him a bigger one, thinking that was the problem, but this morning he was dead. I just bought 6 new ones from another place and want to keep them alive, but am scared this is something contageous! HELP!!