I kept mine in a 20 gal till he was 9" that took all of 1.5 months from 1.5". My friend has one in his 20 gal that is moving soon, his grew from 2" to 8" in 2 months. IMO they need a little more room front to back than they are long. Tanks end up broken if they don't have enough turning room. I never understood how powerfull these fish are till my big hybrid moved a 200 lbs rock over a foot one night. Tank buster is the best term I've ever heard for them. Been several members on here since I have joined with cracked tanks because of them. Best to move them before something happens. For now though he's fine in a 20 gal.