Under Construction! This is an evolving article that is currently work in progress. If you are interested in helping us please use our contact form or pm me to get in touch. BLACK BRUSH ALGAE (BBA) Synonyms: Black Beard Algae Description: Description Here.. Cause: Low/fluctuating CO2 levels, Not enough water flow. Treatment: Add more CO2, Stablise CO2, Trim, Fix water flow, Treat with Excel/EasyCarbo.