Identifying corals resembling fish waste

[RustyPin]

Caught my acan trying to snack on my yellow tang's waste this morning, pretty interesting sight. Not too concerned since my tang's diet is solid, assuming that cancels out the weirdness. Made for a decent pic though.

[heroix]

I wouldn't say that's perfect food for them though. I mean, my tangs do eat each other's poop sometimes, but that doesn't mean it's a good thing.