Biology a question

[rossb]

Well I had a look at the crab and it is pretty ripped up. I originally thought it was molting but on closer inspection it had its shell split open. It was alive and fine yesterday. I removed all of the rocks from that side of the tank, and put all of the ones with holes in them in my sink (they are almost all the ones I bought rather than made). The rest are in salt water in my mixing tank. So any ideas how to flush this guy out with out hurting the rocks?

BTW I have had 3 bits of advice and 3 offers to take it if I can keep it alive.