within 2 years I had 2 Balas grow from 1" to 5.5 and 6.5 inches in a 30 gal tank.
FWIW, Balas are schoolers, they need to be in groups of 6 to be 'happy' ... However, you can get away with having 2 and them being happy... But you really need a bala friend for your bala...
Then save for a bigger tank, they'll need the room. soon.