I just got 2 lil parrot fish one is about 2in and the other 2 3/4in. The bigger one is a bully chases the little one around the tank all day. Thr owner of the aquarium shop I went to told me that a 30 gallon tank is big enough for them but after reading online I now realize that they will need a larger tank. I know there is no exact answer but Approx. how long until they will need a larger tank. I have no other fish in the aquarium.