I got rid of BA in a 120 by adding 8 emeralds, cutting skimmer back to run extra dry and somewhat inefficiently, and finally started dosing fuel to encourage a Cyano outbreak. To make a long story short thr cyano covered the BA covered rocks and after a couple weeks the BA could be pulled off the rock in giant clumps with the greatest of ease. The emeralds cleaned up the rest. Just make sure u he only female emeralds and that you yank them after the BA is gone.