What type of tank set up do you have? What are your water readings? Are you using a wet-dry or carbon? Do you have a gorund probe installed?
My feeling is that a variety of GOOD foods is best. Take a look at the FAQ thread and the receipe there. Of course, a tang needs high quality seaweed foods. Forget about using flakes, pellets, etc. That is for goldfish, not marine animals. Use zoecon as a food supplement soaking your fish's food in it, or, if you decide to use fresh seafoods, you can just add zoecon into the food as you food process it.