1) E.M. (API), erythromycin
2) Maracyn (Mardel), erythromycin [NOT Maracyn II]
Follow the full dosing instructions on the box even thought the BGA will disappear after a day or two. This will insure that the stronger strains of the BGA will not come back and become resistant to erythromycin.
Erythromycin WILL NOT affect your biological filter, especially if you tank is well planted. It is SHRIMP and FISH SAFE.
You do not need to do a blackout if you use antibiotics.
Also try to keep your nitrate level at 10-20 ppm to prevent it from comming back.
KNO3 is a good source...