I think you're on the right track. CO2 is usually lower than we think/test.
My 200l tank is set at a CO2 concentration of between 40 and 60 mg/l depending on which pH test/probe I use. When it was set at what I thought was 30mg/l I was also getting some BBA. Increased the CO2 and BBA stopped growing and no adverse reaction from the fish.
Another suggestion I have is to raise your NO3 levels slightly. I usually keep mine around 15 to 20 mg/l.