The one inch is a good rule of thumb, but when using that as your decision for fish you also need to think about the nature of the fish. Balas from what I know prefer to be with at least one other bala, more is better. Like previously said, they are very active fish. I know he looks small and kinda darty now, but you will see in say 6 months depending on feeding/maintenance, that they need long distance tanks. Plus, when you see a couple bombing through a 6 footer or longer its a pretty cool sight. I would love to havea 10 foot tank just to see them have an oppurtunity to open their speed up a little