I don't have a yellow tang but found this on the internet.
These fish are herbivorous need vegetable matter in their diet. Algae tablets, lettuce, seaweed and spinach all make good foods. They will browse on algae growing on rocks and other decorations
I have read that some will eat anythng in front of them.
Your tang (any fish) does best with a varied diet, not just flake.
To soak flake in garlic take a bit of water from tank, mix it with garlic extract etc and leave flake to soak.