Hydrogen peroxide treatments can be effective. In a nutshell, you shut off any pumps and filters, use a plastic syringe to spot treat the affected areas, let it sit for 15-20 minutes, and then restart the pumps/filters. After a few days the BBA will go through a series of color changes as they die off.
Mind you, this is a short term fix. It may come back unless the underlying cause is addressed.