I swear by nori. I put a quarter sheet folded 3 times in a lettuce clip daily. I have the fattest, healthiet looking tang I have seen. I have a few other fish that pick at it but the yellow tang is the biggest consumer.

He does feed nori:

It's not enough.

Something else is missing.

Serve Frozen Formula 2 (I think that's the algae based one). Cut the food up smaller... Soak it in selcon and garlic... Turn off the power head when you are feeding so the food moves slower...

You said he's going for it, but can't quite get it down...

maybe this will help...