Smelly?

My crabs that are in the ISO tank smell like the ocean. I don't know what it is, at first I thought it was their food, but I changed their food and dug the left overs out of the substrate and put them back in and they smelled a little better, but still like the ocean. Its weird. I hope one of them is not on the verge of molting, because I have heard that they sometimes get this smell when they are about to molt. The problem is that I don't know which one it would be. I checked for the signs of premolting symptoms last night, but I saw none. Well, I guess I should just keep a close eye on them.