There is a Golden Headed Sleeper in with my 8" Derasa for the last 5 months. He is always dumping gravel on the clam. The clam does not seem to care. If the gravel gets too much the clam starts expelling water and cleans himself off. Sometimes I go in and with a small turkey baster push the gravel off. I also have to do this to other corals in the tank. I do not think this is bad for the clam. In nature, the clam is getting sand and stuff all the time from the currents of the water and gets by.