Yeah, I'm not worried about it as the clam is just fine during the day with the MHs on and the clam is no worse for wear. The tang is definately attracted to the purple rim going around the mantle, but only when the actinics are on.TXLewis said:Could be that over the course of the day, some filamentous algae has grown near the mantle (this seems to happen in my tank) and the Tang is going after that. I frequently see my tangs cleaning stuff off of the shell of my Deresa - but no damage has ever been done to the mantle. If yours isn't damaged and the clam isn't retracting (not that it matters if it does once the lights go out) then I say don't worry about it. Of course this is my non-expert opinion...