I kept a tang in a 55g and for the first few months he looked great, but after about 2 months he became less active. He also went from eating a sheet of Nori(sp?) a day to hardly touching it. I gave him to a freind that had a 200+ gallon tank and almost over night he turned back into the fish I first baught. Just my 2 cents, but as for me I would not keep a tang in that small of a tank, but that is just from my own experience.