Andy is right. It's all about stress and a understanding about the various habitats surgeonfish inhabit. Some tangs, like yellows, cover large areas of the reef in flocks, like birds. Some, like the clown tang work surge zone areas that are highly oxygenated and needs a fish that is full of energy to cope in that environment, one reason they are bad choices for most reef tanks. (I have one, he is a jerk)
Kole tangs, for instance, tend to be more solitary and restrict their browsing area to a smaller portion of reef, so they tend to adapt to aquarium life better.
The tank itself can prevent stress. My tangs are 10-20 years old. Never any ick. There is a lot of common sense and thinking like a fish (yes, really) that goes into a tang friendly tank.