Hole in the head

[naesco]

Ammonia?? How long has it been since your tank cycled? How many and what fish do you have in your tank?

Although tangs like non veggie food from time to time all tangs except the blue tang need algae to live and grow. What is the first ingredient on the NLS pellet label. It should be spirulina.
Go to the LFS and buy Wardleys spirulina discs or pellets. Wardley because it is spirulina.
Go to an Asian market and buy non flavoured nori.

You should be dropping in a couple of discs at least twice a day and have some nori on a clip.
Tangs feed all the time throughout the day.

It is important to use garlic extract when you add a tang to ward off ich but I would not be using it and the other stuff daily. Use selcon soaked food now and than.