If its a parasite that is causing them to scratch like they are a fresh water dip should do em wonders. I do have a clown and a fire fish who routinely dive into the sand bed and surf along it.......I dipped em both, numerous times, and continue to sand surf, but best I can tell is its just their way of stirring up the sand bed and looking for food particles.....Scratching on rocks is another thing altogether though and I would certainly suspect parasites. That is unless yur water parameters are out of wack, as bad water parameters can also cause em to do things like that. So make sure your parameters are good, and then if they continue on rubbing against rocks etc do a fresh water dip.