Excel is excellent in ridding you tank of BBA. I would try the extra circulation as a long run cure but zap it with Excel. Turn off your flow when treating and target the BBA specifically with a baster or syringe.
I have heard that BBA likes high flow, I am no expert but it seems to pop up right in my HoB
outflow. I had to do a ton of manual cleaning including scraping the top off my substrate last time I had it bad to get rid of it. =/