Spot treating with Excel will work for BBA. Have to anubia that I just knew were going to have problems with being too close to high light areas. I spot treated them once with Excel. Be sure not to overdose your tank, its easy to do when spot treating. I used a syringe with double the amount of Excel I use daily and slowly squirted the plants. By the next day the BBA was turning pink/red which meant it was dying. Snails are taking care of the rest. Another thing to be aware of is certain plants are sensitive to Excel and can cause them to melt. I know Val's are one, some say crypts too. I have corkscrew val and tons of various crypts and haven't ever had problems with melt due to using Excel. As for BSA... some say Excel will work on it and some say no. If your spot treating for it you can try. If you have alot of BBA then you have to treat an area at a time. You can't just spot treat the entire tank or you could grossly overdose. Cutting your light hours down and upping CO2 should take care of it. I recently cut the hours down on the metal halides, went from 8 hours down to 6, then slowly have been upping my daily dose of Excel to increase available carbon for plants. Excel isn't CO2 but it helps alot. I believe too low a level of phosphates can also contribute to the problem so you might want to test your water also.