I recently bought a green terror,and the first day i got it he is already eating beefheart and pellets.He resides in a 55 gallon.Will i eventually have to upgrade,or is a 55 good enough for one.He is around 5 inches now,and is very interactive.
It would probably be ok as the bare minimum for a lifelong tank, but when he starts to grow and bulk up you might feel guilty that the tank is too small.
a 55 is a good start for him. if your sure its a male then a 75 will be appreciated as the extra width will provide more comfort and the possibility of cichlid tankmates depending on his temperament.
I kept a 8" green terror in a 55gallon with a few smaller fish (convicts and cryptoheroes) and he was fine. He came with a tank so I just wanted to get rid of him but if I were keeping one personally I wouldn't keep him in anything smaller than a 60gallon for life, but a 75 would be better.