Ahhh, BBA. That one is a demon my friend. I used high doses of Flourish excel (I think it was twice the recommended dose) to kill it. But it also killed my Elodea plant. There is also another plant that can be killed by it but I never remember its name. PLUS you should dose carefully because if you dose higher than twice the recommended dose it could kill fish too. But I was battling with it for a few months until I decided to try excel and bingo. If I were you, I would give it a try. I almost wen crazy with that stuff. I know how you feel. Good luck there.