Well these fish needs a mix of meaty foods and greens. Nori is the best option for the greens. It is compressed seaweed you can get at most LFS
's, asian food stores and even many grocery store. Just pick up a clip at your LFS
and clip a strip in there every day for him. Or you can use a rubber band to attach it to some of your rock. They will graze on it. The coral Beauty will also pick on algae if you hace live rock.
Here is a pic of my Heni's grazing on nori attached to a clip.
As for meaty foods which I would suggest Ocean Nutrition and San Fransisco brand frozens. Many good choices from these 2 companies. Just stay away from brine IMO