Even though tangs are herbivorous, they still need a large variety of food. It’s best to provide these and other algae eating fish with different types of algae, along with other food types that are algae enriched. Don’t just buy a sheet of green nori and expect your fish to thrive. Give the fish green, red, and brown algae, along with meaty and omnivorous foods enriched with Spirulina and other vitamins. These foods will boost the fish’s immune system and promote good color.