I think this is green spot algae. Tank details, using EI fertilization, co2, 65k high light 8 hours a day, weekly 50% water change. The algae does not come off if I scrape it with my fingers. I have increased the phosphate (KH2PO4) in my EI mixture, I would normally use 4.7 grams and have increased it to 15 grams for the past 6 week with no noticeable change. Any thoughts, help, suggestions would be greatly appreciated.