You can buy acid at the drugstore - ask you pharmacist. Or try a swimming pool chemical company. I have a large, beautifully colored Lion's Paw (_Lyropecten nodosus_) that has some coral growth on the nodes. Does anyone know what it would do to the shell if I tried to grind it off with a Dremel tool? Would the shell be damaged underneath? It is in perfect condition except for that. Sylvia Edwards