The clam doesn't look too bad to me. I don't freshwater dip a clam unless I absolutely have to. If the clam has only been in your tank for 1 day, I'd give it a couple days to settle in. Make sure that it's not in an area of water flow that may be too strong. Is it getting enough light? Did you check the clam for predators, ie. pyramid snails? Are all you water parameters ok? No fish in your tank nipping at the clam? My Chevron tang targets one of my Maximas alot. I had to use a dead gorgonian to hinder his access to the clams mantle......it's worked so far. Anyway I've just tried to list a few things to check first. Freshwater dips are sometimes necessary, but dipping does stress a clam.