I would remove by hand. Take off and leaves affected and remove decor from tank if trying to scrub the stuff off as you will see more of a problem if the bits start floating around.
I have heard overdosing excel has worked for some but also it can cause die off of some plants, especially vallis. I have never used it and do suffer from BBA but is controlled if you don't overfeed and remove a little every night during normal daily maintenance.