How big can you grow a fish in a 6ft tank?

[Aquattro]

Well, a Vlamingii Tang can hit 24" in the wild, so I would say minimum 12" in captivity, all conditions being met. Now, can you maintain proper feeding and proper water quality? That's a tough one. If he's grown to 5 inches in a year, iI would guess you might see 10" eventually. Typical aquarium care, you might see 8". Unfortunately not a lot of people have these, so it's hard to get "from experience" feedback.