IMO & IME: you cannot get a fish that refuses a variety of foods to eat by just offering it something else. If this fish won't eat brine or mysis, its doubtful that he's ready to eat anything. Even though tangs are herbivores, they will almost always eat meaty foods before veggies and a Hippo is really feeds a lot on plankton in the wild. Of course you want to see your fish eat; but I think you need to look at more than just what you're feeding him. You did post SG ,but, what's the water temp? Ammonia/nitrite? Does he have a quiet place to hide? Its impossible to guess what could be wrong without this info. These can be hard fish to acclimate and your description of him sounds like something is wrong. Again, IMO & IME, he doesn't have a problem because he hasn't eaten yet; but may have a problem that is causing his not eating. (If that makes sense)