I doubt you fish grow anymore, fish will never reach they're max size in captivity. no matter how big of a tank we give our fish the environment is never the sameNot arguing at all. Just saying that if my fish were as big as yours, I don't think I'd feel comfortable keeping them in my tank. I don't know how long it'd take for my yellow tang to get to be 8 inches long, but I suspect I have plenty of time before I have to upgrade.