We feed our Yellow Tang (& Purple Tang, & Hippo Tang) the following ....
Our homemade food
Nori on a clip (we get it from the site the FF referenced)
Dulse (another type of seaweed, also from the same etailer)
baby spinach leaves
organic romaine leaves
OSI Spirulina flake
OSI Spirulina nibblers
Obviously not all at the same time.
The tank gets fed our homemade food daily, and we offer Nori, dulse & the lettuce/spinach on a clip 3x-4x week. Heavier on the Nori/Dulse, light on the spinach/romaine. All "clipped" food is soaked in Zoe vitamins.
Other stuff (spirulina flake, etc.) is offered sparingly maybe once weekly.
I truly believe that a varied, vegetable-based, vitamin enriched diet is very important for Tangs. Both our YT & PT have been with us over 4 years now.