Tangs are cruisers. they constantly cruise the reefs. Most other smaller fish tend to stick around their 'home'. But if you've ever dove on a reef with tangs, you'll have seen them constantly cruising. Putting them in too small a tank, specifically lengthwise, limits their ability to roam. Like having a greyhound as a housepet in a small appartment. The environment may be ok for a small mopdog/lapdog, but its cruel for a greyhound.
I have a 110 gal
, 4 ft tank. Larger in volume than the 5 ft 100 gal
tank, but less suitable for a tang. That's why when you look at minimum tank size for tangs, look at it from a length perspective, to actual volume. I would not put a Yellow tang in my 110 because the 100 gal
Liveaquaria reccomends is that 5 ft tank.
BTW, younger tangs cruise just as much as the older larger fish, so please don't say I'll move him when he gets bigger. I dove in Hawaii and there were NASO tangs. The large ones were cruising along the reef, while the smaller ones were darting along with them.
Of course you get to make your own decision, but if you try to keep a greyhound in a small city appartment, don't be surprised if we get a bit pissy when we hear about it.