As fish keepers, we have an obligation to provide an environment where fish can thrive, not just survive.
Keeping a fish in a tank that is to small is not right. You have to account for adult size, and get as close to it's natural habitat as possible for it to display normal characteristics.
Some fish naturally live in schools or groups, such as bala sharks. They also get very large and need free swimming space. Keeping them in an excessively small space causes stress and premature death.
Please do us all a favor and find your bala a new home, as should neighbor. Thanks.