I've never had a problem with fish wanting to eat, but I used garlic flavor enhancer when my Tang was getting black spots. The fish would indeed go nuts over it.
But after using the garlic enhancer, though, the fish seemed less interested in feeding for awhile when I stopped using it. Kind of like eating at a 4-star restaurant every night, then having somebody show you dry bread and water.
I had to get some nori from a local "kind" type of grocer - its the stuff they wrap sushi in, shouldn't be too hard to find. Before I started feeding him that, I was using several kinds of prepared seaweed from the LFS, and my tang was developing a mild case of HLLE. Since I started giving him nori daily, its improved (which I hear is rare).
I avoid brine shrimp, after being told its the equivalent of junk food, with little nutritional value. The inland lakes' MYSIS is like 90% protein, and my tang loves it. He'll eat anything now, flakes, slow-sinking morsels, algea wafers (if broken up into bits), even a little squid.