[jmowbray]

Depends what is near it.

With the filters off hydrogen peroxide spot treat destroys bba after 2 doses 6-12 hours apart.
Excel is much less effective in my experience.
However if bba is near HC or moss I don't a lot treat with hydrogen peroxide because I almost always end up killing loads of it.
At that point I cut, use tongs to pluck it off and then either do two or three x daily hydrogen peroxide spot treating with filter on or excel with filter off.

I have also experienced the same thing. H2O2 works best for me.