Good question. I still wonder with that. I feed them up to three times a day (if I can), but also frequently skip a day. I give them so much as they can eat in less than 1.5 minutes. It is a little ennoying, every time I show up in the office (where my tank is) all the fish line up in front of the glass (instead of nicely roaming along the rocks). Don't know if anyone has a trick to avoid that.
Also, I seem to cut down on feeding when green algae appear faster than normal (meaning, if I have to scrub the front glass more often than every three days). However, if I cut down on the feeding, my black-bar damsel start to pick on some polyps. I don't like that either.