I have a Yellow & Hippo tang in my clam tank, they have never touched one. New clams with a little algae on the shell will get a nice cleaning from the Tangs, but that's all.

Someone (I think Larry/Instar) mentioned in the last meeting that Copper Band Butterflies will pick on Clams set in the sandbed, but not if placed on the rocks. Don't know why, but an interesting tidbit. Have no idea if this applies to clam eating Tangs ... maybe worth a try?