Anything that irretated the clam will cause its mantel to "pinched". Pinched Mantel Disease is a specific disease. If this is the cause for you clam to not do well and have it mantel pinched, then FWD is recommended and is very effective.
Dick Perrin the owner of Tropicorium routinely dipped his clams prophylactically (this was in the late 1990). I got the idea of treating clams with PMD using FWD from talking to him. I was trying to teat a tankfull of clams with PMD in, or about 2001 when no one know anything about PMD. I was desperate as my expensive and lovely clams was slowly dying. I was good enogh of a reefkeeper to know that my clams are not dying due to poor tank condition, rather, it was because of this deadly disease. Untreated PMD will kill a clam.