Much has been written about how to get rid of BBA in an aquarium. The techniques you'll find have different levels of success and come with vary levels of risk to your fish. Three commonly suggested approaches include: spot-treating with hydrogen peroxide and/or Seachem Excel; dosing the water column with hydrogen peroxide and/or Seachem Excel; and a 3+ day blackout.
I have a heavily planted tank, so the blackout idea seemed too risky. I also have a number of fish that I didn't want to risk with a water column treatment. So I was left with spot treating which has been effective on the particular spots I've treat. The problem is that I have more BBA than I can treat in a single day. Not to mention that spot treating doesn't seem to be 100% effective. So in the end, the BBA grows about as fast as I can kill it.
Luckily, 99% of the BBA I have is on my driftwood and eventually I had the idea of placing small bags (see images below) over the wood and squirting 10-30 ml of hydrogen peroxide into them using a medication syringe with airline tubing attached to the end of it. The bags:
After a treatment or two, the BBA would turn red. Just to be safe, I would do a third treatment before removing the bag. Once I removed the bag, the BBA was eaten by my otocinclus and garra. Eventually the wood was free of BBA either from falling off or having been eaten.
Check out these related articles: