I don't remember the brand - to many years have passed (back in 88-95)since I kept marine fish. It was heavier/thicker than a flake but not a pellet. I had Imperator that had it when I got him. Took about a year for the erosion to go away. I had him from 91-95 when we moved. I fed the tank spirulina, fresh (squid,shrimp,clam), community marine fish food. The spirulina and fresh ingredients would get the selcon soak.
You should be able to find spirulina in one form or another I would think at any of the fish stores. Also a lot of the blended foods for herbivores have some spirulina in them.
I'm not saying don't use nori - I would just try the spirulina in addition to the nori (variety).
I think no matter what you feed them the selcon/vitamins are important.