a tang in a 12 gallon...even if it is small im guessing its about 1.5 -2 in. long i mean you may be lucky if you keep it for 3 weeks tops i had a buddy who thought they could keep one that small in a 20 gallon with the tank being over a year and a half old and it died 20 bucks down the toilet. i would take it back and get a yellow clown gobie maybe or another clownfish and let that be it.
Im just going to shake my head on this one means you are wasting your time if you think it will get bigger and you will take it back just to exchange it for another one. plus you can not take back a dead fish