He's posted about this in another spot.
The fish in question are in a 60 cube, which is far too small for the tangs.
Remove the tangs and put them in at least a 180g tank. They need the space. What you are doing is equivalent to locking three large dogs in a room and never letting them out. They may not be fighting now, but they will.
They will continue to nip the shark. You may not see it, but they will. Next time it could be the eyes, or the shark could die of infection from having its tail nipped open every time it grows back.
Your shark will need a much, much bigger tank. Start getting that tank now so you will have it ready. You cannot keep it with any fish that nip at rocks, as it will be tormented again. You have been told this.