Erik
Soaking food in garlic will help to boost the tang's immune system. I would definitely place a light above the tank, as I think it is important for any critter to have a consistent day night, or light dark cycle. And it only needs to be a dinky NO fluorescent light fixture. It wouldn't hurt either ... it would allow you to observe your fish carefully; can't really do that with no light over the tank. Also, be sure to put a piece of PVC in the tank to give the tang a hiding spot.
Phong, I believe if a display tank is literally fish-less for at least eight weeks, the ich will cycle out of the aquaria due to lack of a host.