How big is your system? 56 gal DT, 10g sump
Are you running any kind of fuge at all? CPR small hang on, just a couple gallons with a rock, chaeto, and some kind of fuzzy algae; crawling with mysids, snails, pods; I give the chaeto a shake every evening to hopefully send some stuff to the DT.
Are there other inhabitants that may be competing for the food source in your tank? Yeah, one of the reasons I worry - melanurus wrasse and cleaner shrimp (steals when I try to target feed the mandarin)
Youve said that he seems to be grazing around does he just glide around the rocks or is he stopping and pecking? He is always pecking, I'd say he gets something at least every 30 seconds or so.