When first starting out I added a small yellow tang to my 46 gal. befor researching it. I added it thinking that if you had a saltwater tank, you had to have a tang (plus, if they aren't good for my tank why would the fish store have hundreds of them). This mistake made me vow to never purchase anything I haven't researched thoroughly, which I have stuck too.
Oh, why was it a mistake...? Tangs grow fast, too fast. It had soon become too large to be happy in my tank. Unhappy tangs are susceptable to ich - boy was that a battle. Big tangs eat alot, an awful lot. Which causes alot of waste, too much waste for my little 46, nitrates outpaced my DSB causing algae. When I finally figured out I needed to sell her I found out that Tangs are damn hard to catch in a reef tank.