You have a marine fish with hole in the head disease???? That I've never heard of. Can you get a photo? Are you sure it's not lateral line disease???
Hole in the head is a bacterial disease of FW
fish, often spurred on by poor water quality. Live tubefix worms have been taken off the market many years ago because of it's relationship with that same bacteria.
Tangs are suceptible to lateral line which is pretty much caused by a lack of proper nutrition and can take months if at all to completely heal up. Here are some questions....
How big is the tank?
How long ha it been up and running with fish in it?
What type of filter?
Is there a protein skimmer or refugium?
What are the current results for ammonia, nitrite, nitrate, pH, and SG
What are you feeding?
How much are you feeding?
How often and how much do you change water?
What other fish reside in the tank?
Does the tank have live rock and/or live sand?
Does the tang have any whitish line broken or solid starting to run down the sides from it's head?
We, as a people, know so much more about outer space than we do about our own oceans. This lack of knowledge can very well spell the dangers that lay in wait for us.
The oceans surely would swallow us before a rock comes down to smite the planet of it's life.