Nori and garlic is a good start but is not enough, IMO. Get them eating NLS pellets before you turn them loose with the rest of the tank. Vitamin A, E, spirulina and the other good stuff that they put in there really helps to keep disease down too, including HLLE, flashing and all of that.
I will also warn you that large tangs can/will eat coral. You can literally come home one day and hundreds of your polyps or most of your acans can be gone. Here is a shot of about half my FO from a few years ago - the island of misfit tangs. The black, 2 of the purples, the PBT, hippo, yellow, atlantic blue and definitely the sailfin all ate coral and were donations from other ****ed off reefers. The chocolate, the flagfin (amazingly) and one of the purples did not eat any coral. The Huma-huma was more coral safe than the tangs.
Here are a few more teasers since I dug my album up - these were fine in my reef.
Black x Scopas
Achilles x Goldrim
None of these fish had any issues with disease (including the hippo) and fish came and went out of this tank all the time. I fed about 50% NLS Pellets, and then equal parts of nori, formula 2 pellets and PE Mysis (I think that the off-brand kind is near worthless). If you don't feed them enough, then they can get sick too.
Sorry for the novel.