when my snapper gets algae I use a little plastic scrub brush on him since he's about 6 inches across. But if he's shedding he's more sensitive to it and really doesn't like it. So when yours gets to a shedding phase I would just let it go, it'll fall off by itself. You'll know they're shedding by the tiny pieces of skin hanging off all over. Mine looks like a little old man with a beard when he's full blown. Pretty funny actually. Otherwise the scrubbing won't hurt them.