I respect your opinion and I agree a 6 inch tang in a 4 foot tank would not be appropriate. Very rarely will a yellow tang get that size in a home aquarium no matter how big the tank is so I prefer to give advice based on the vast majority rather than the very small minority of experiences. I have been to a lot of houses and a lot of public aquariums, and the vast majority I have seen are 5'' or less and perfect for a 120g tank.
I have had mine for close to 10 years and it is still appears to be a bit less than 5''. It does give hell to other new tangs on occasion when I swap them out (not every time), but that only lasts for a an hour or two if it does happen.
It can take decades to get to max size yes (As in they live for 40+ years in the wild) so it will eventually get to 7” but it may take years. I’ve never kept these tangs but I had to put them in the 4’x2’x2’ holding tank in my LFS and even then they were aggressive. I got in quite a few 4-5” yellow tangs and they got to 6” and looked giant (You have to remember their dorsal fins aren’t like the Acanthurus tangs - They get big). Also - The small yellow tangs that are the size of a dime grow a lot quicker than say a 5” tang.
I also agree with the last paragraph you wrote but if you think about any fish, no tank size will ever compare to their ability to roam and grow when in the wild.
I know that but the biggest tank you can get would Atleast get close to that ability - I saw a 4” YT in a 5’ tank and trust me, that thing did not look small when it had its fins out. Also, other tang or not they will be aggressive to anything new (Or even old). As soon as aggression gets too bad and pacing begins, you’ll know it’s time for the tang to be removed. I know people have had Achilles and the harder tangs in 4’ tanks and had success but that’s hard to get unless you’re prepared for the ich to battle - In smaller tanks tangs get ich much faster.
I have read tons of people having healthy and successful YTs in a 4x2x2. However, I agree its inhumane to force a tang to live in an environment that it is too big for. But 4' should be plenty of room while its young and if it outgrows the tank then I have no problem taking it back to the lfs. It is also going to be the only tang in the tank even though Ive also read people keeping multiple in a 120 successfully.
Usually that 120 is a 5’ display tank which is why people tend to have Success having multiple (Although, I don’t recommend it because that’s 3 7” active fish in a 5’ tank, almost 2’ taken by YT). If you stick to the thought of one yellow (And don’t start mixing Zebrasomas) yes you could keep one until it gets to 4” but I still wouldn’t put a tang from the larger families in a tank less than 6’ because of how much they truly use that space.
You can get away with things like clownfish because they don’t claim a 10’x10’ square in pairs, they usually claim a 3”x3” square. Tangs claim everything and anything so just be warned, peaceful fish with a tang tend to go wrong so if you find a fish you like then go for that however, the Foxface and tang will go after the same food and compete which tends to go wrong in small tanks. Basically, algae eaters with an elongated snout go after the same algae’s but I have my algae eaters working out because they don’t chew the same algae (One goes for macro & GHA - Foxface, the other goes for film algae - Twin Spot Bristletooth). Bristletooths are alright in 4’ tanks because in the wild they don’t spend hours along a reef, they just swim in patches which is often why they do better in a 4’ tank than an active “demon” like the YTs.
I say demon because when they get too big for that tang aggression gets too much, they will murder and they will do it no matter what, even if they were added last they will still murder the fish when they’re too big for the tank (As the fish grows, so does their territory). The easiest way to stop the murder is get rid of the fish just before it gets to max size or, get rid of it just as the small bits of aggression begin.
Blue tang
Marine Beta
Canary Blenny
Fire fish
I’m sorry, what?
If that’s Paracanthurus Hepatus you’re talking about, then I have an issue - That tank is half of their minimum tank size. With this fish I don’t care if it’s the size of a dime, it grows FAST to get to 1’. It’s also active, one of the biggest ich magnets in that family and gets to 1’. Even people with an 8’ tank have these guys and it still looks big in that size tank.
If you mean Acanthurus coeruleus then I’d still say you’re 2’ off what it really needs, these guys are also fast growers (Not as fast as P. Hepatus) but they will get big, their in the most aggressive genus which just tells you what they will become. Again - I’m just giving my .02% of experience (I have done a similar mistake with P. Hepatus before - 10 years ago).
