[Myka]

Could you put a fish in the tank to help eat the pods? Dottybacks and Wrasses do a fantastic job or maybe a Mandarin if the tank is suitable. I like to have a Halichoeres wrasse in with clams (and SPS) to help keep irritating pods and worms in check. Yellow Coris are a good choice for smaller tanks and tend to be invert safe too (which most Halichoeres aren't).

Pinched mantle usually shows up just in one or two lobes at first, you may indeed have a case of pinched mantle. It's hard to say at this point from the pic. With pinched mantle it is best to act sooner rather than later. A FW dip will not hurt the clam whether or not it has pinched mantle provided you take the appropriate steps to match pH and temperature. Use a digital pH meter for this, drop style test kits are not accurate enough.

"I have crabs" link is good information.