Proper size for tangs?

[DorySaid]

Ideally, I would say 180 or larger. I've had tangs in a 90 gallon before. But when it comes to longevity and overall health, I think you'd be better off with the biggest tank you can afford/accommodate. Also I wouldn't recommend stocking the hell out of it with live rock and corals to allow the extra swimming room that you intended by setting up such a big system.