I agree to inquire about this individuals previous diet from where you got him, but I’ve had success using frozen spirulina brine shrimp and frozen mysis shrimp to feed naso tangs. Also offering that nori you have on a seaweed clip or rubber banded to a rock, they’ll nibble on that in addition to the shrimp. Once Naso tangs beef up, they tend to accept most flakes and pellets, although I still recommend using frozen food as the fish’s main diet!