BBA is nature's way of telling us we don't have enough dissolved CO2 in the water for the amount of light we have. If you have tried doing a really thorough cleaning, and pruning to get rid of all traces of BBA, and it still comes back, you just don't have enough CO2 for the amount of light you have. You can either work on the CO2 or decrease the light.
To get more CO2, without killing the fish, make sure your tank water is very well oxygenated, by setting up the filter outlets and powerheads to ensure having the whole water surface rippled, not splashing, but getting close to doing so. Then, to really be sure, install a wet/dry filter, which does a great job of dissolving oxygen into the water. With well oxygenated water, the fish can live with much more CO2 in the water, making it less of a gamble to increase the CO2.
Don't rely on a drop checker or bubble rate alone to determine that you have enough CO2. You need to slowly increase the CO2 bubble rate, a little bit at a time, then wait while watching the fish and plants to see if the plants respond favorably. If they do, and, of course, if the fish don't show obvious distress, slightly increase it again, and repeat the watching. It works best if you watch the plants for a few days to be sure they are responding. Once you reach a bubble rate, where a further slight increase doesn't do anything for the plants, you have the right CO2 bubble rate. (This can only work if you are dosing more than enough of all of the nutrients the plants need, so only the CO2 and light are determining how fast and well the plants grow.)