I was able to keep one in a 180 gal for almost a year, but even that was too small. He ruled the tank and zoomed around the tank all the time, but eventually died. they live in the high current regions of the sea, so if they don't get the oxygen/exercise that they have evolved to need, they die.
I had one (3 inches) in a 140 gallon FOWLR for a year. He did well. Ate NLS pellets, Nori, and even flake food. He just started to become more aggressive to my Regal Angel so I sold it.