i would not do a fresh water dip on the clam, this is not what pinched mantle does to clams.
you have two fish that are notorious clam nippers, the flame angel and bicolor blenny. try and place something over the clam to keep fish away but still allows light to get to the clam, like a strawberry basket or the top of a clear 2l bottle with a bunch of small holes drilled in it so water can still flow through it.