They are very hard to get eating, but once they start, they never stop. I actually built my tank around one. I had a tank crash early on. So when I got it running again, I left it completely empty except for some surviving corals clams and some inverts. It was getting to the point that the algae was taking over, and the pods were going to mutiny from over crowding. I then added my PBT and my leopard wrasse. Neither ate prepared foods for a week. But I could see them picking at the rocks and eating. I tried every frozen food, prepared food and live food you could imagine to stimulate their feeding. Finally one day they ate mysis. From then on, they would take anything frozen. Took another month or two before he would take nori. He will only eat green nori, he will not eat any other kind. He will not eat macro etc etc.
I did initially run a UV for 3 months afterwards. He has had two spot of what I thinki was ich one day, but never really did know. He nibbles on frozen cube right out of my hand now.
He has been a real challenge, because they are very aggressive, harrassed my poor lawn mower blenny for weeks before he would let me be out in the open. He will harass ANY fish I try to put in there!
Keep trying, but really I think you have to have a tank free of other inhabitants and high natural food population to get him adjusted to the tank so he will start eating.