Is there a way to scrape it off leaves? I don't know if I should cut the big anubias leaf off. I'll definitely try trimming the repens though. IF I had to resort to phosphate, do you know what I'd need?Before tinkering with phosphate levels and additives I suggest if you could just scrape out the GSA, cut out the leaves with gsa followed by large water changes. Try this for 2-3 water changes and see if it keeps coming back?
I had GSA in my 30 cm cube and this method worked for me. Now I have some Green dust algae in my tank but no relapse of the spotted variety.