If you MUUUST have a yellow tang, I'd consider removing him until you've finished stocking all other fish.
They can be nasty buggers, especially to newcomers.
Best suggestion IMO
. Return the yellow tang. Get either a midas blenny, canary blenny, or yellow clown goby. That way you get yellow in your tank and not have such a big (drain on the bio-load) and mean (drain on other's immune system) fish.
Consider a small kole tang maybe.