I wouldn't worry about it. He's still fairly young. It should start to get a little less as he gets bigger. For now, it just means he's not done growing (especially since everything else in your tank is doing well.)
BTW, I've looked everywhere for an ID on that crab, I can't determine what it is. I posted it on another site I use to see if anyone can ID it there. You may want to try asking WetWebMedia.