I'm watching one in my display as I type this... He spends most of his day banging away at the liverock, studiously avoiding any corals or even macro-algae, but scraping off film algae and scraping up the coralline. (He also ignores the hair algae on the back glass.) As for feeding, this guy started out very daintily sipping the tiniest specks of food in QT. A whole frozen brine shrimp was just too big, but a capelin egg or a busted-off swimmeret from the tail of a mysis would be taken, along with small pellets and flakes. Now, there's very rarely a piece of LRS or Rod's Food that he won't chase after and take down, right in there with all the other fish at feeding time. He's easily the biggest fish in my 220, but aggression is rare. Sometimes a short chase after a fairy wrasse, and I once saw him try to swim with a Talbott's damselfish who was having none of it. It looked like that video that circulates on Facebook, of a baby elephant chasing guinea fowl around at a zoo. No harm done, but the damsel got tired of the game pretty quickly and ducked between the liverock.
That having been said, they don't always acclimate well. A previous one ate nothing, and rarely ventured from PVC hidey-holes in QT. Tried nearly every temptation for a month, only to find him floating at the surface one day. I would look for one that's swimming confidently in the open at your LFS, and if they'll feed it for you, so much the better.
~Bruce
