Hi
I had once an infection of BGA (not much but good enough to bother me). I followed guys here, did some pruning of infected plants, removed BGA from substrate, cleaned the filters that were clogged, improved the flow/circulation & temporarily had a water blasting the BGA sites. As an immediate measure, during the WC when water level is low, I injected H2O2 straight on the BGA, wait a few minutes, and refill the tank. The nascent Oxygen oxidises locally all the stuff (be careful that this is a local effect only). This all helped, and I didnt have to go the anti-biotic way.
I guess that since BGA uses nitrogen fixing for its energy, improving water Oxygen content helps since this hinders their growth. Adding nitrates & good flow further deteriorates their condition. Plus the O2 once formed from H2O2 also helps aerobic bacteria in the filters.
Hope this helps.
-niru