[Hermie's rule]

Try to get sorta a swimming pool that the crabs can almost totally submerge themselves in. Not so deep that they can't see out over the water line but deep enough that they can partially submerge. Yes, sponges are okay in the crabitat. You should rinse them out or else they'll develop funky molds and growth on them. You don't have to wait for dechlorinated water to sit out. Just use it once it's well mixed. I wouldn't use any dechlorinator with slime coat in it. Hope that helps!