Tangs are natural grazers. I have three in my tank and they are constantly picking at the rocks. I feed seaweed 2-3 times a week. Other than that, they find their own food. It is in their DNA. With a little time, I am sure that he will figure it out. As with any picky fish, you might want to start them off with mysis and garlic. As with everything in this hobby though, nothing is guaranteed!