If it is on your plants than there is no way to scrub it off unless you actualy prune out the affected leafs. If its on your tank glass, I've read some people have good results using an old credit card or a razor blade. Personally I use a kent pro scraper with metal blade (not recommended for acrylic tanks) - add a little elbow grease to that and you should be able to take that sucker down!
However in the long run you will need to remedy the root cause of GSA which is associated with high light and low phosphates.
JP
However in the long run you will need to remedy the root cause of GSA which is associated with high light and low phosphates.
JP