All crabs (I believe) require land onto which they can go when they need air. If you can't provide this, you'd better quit getting your hopes up or get another tank for it. Sorry.
I already asked that questino ans got a wealth of info here: http/fish.orbust.net/forums/index.php?sh...l=red+claw+crab. They can't stand ammonia or nitrite so U gotta monitor those closely. Escape artist and as far as I can tell don't bother the fish. They like salt in their water and like to hang right outside the water.