Below is some basic info available via a google search...the one my client has is in a 240 and I anticipate it'll be fine there for several more years at least.
"As I indicated earlier, Vlamingi tangs can reach an adult length approaching two feet. They require a lot of swimming room. I recommend an aquarium that’s at least six feet in length and two feet front to back. Bigger is even better, especially if you’re considering keeping more than one specimen. They are a spectacular sight in groups. Joe Yaiullo maintains a group of Vlamingi tangs in the Atlantis Marine World reef aquarium. This aquarium is 30 feet in length and 20,000 gallons in volume!
Other than space, Vlamingi tangs have no special needs. They look their best in reef aquariums but don’t appreciate being crowded by corals and rocks. They literally eat just about anything, but a good diet should consist of an assortment of meaty seafood. Chopped krill, mysis shrimp, plankton, crab meat, and clams are good sources of nutrition, along with occasional spirulina-enriched flakes and dried macroalage. As planktivores, they should be fed at least twice daily. Vlamingi tangs make good tank mates. They don’t exhibit the territoriality of most of the other tangs and generally ignore other reef fish.
When shopping for a Vlamingi tang, be sure to see it eat. They aren’t picky eaters and should begin feeding quickly in captivity. While not particularly susceptible to the typical aquarium diseases, it’s always best to quarantine a new specimen for a period of at least two weeks before introducing it into a display aquarium."