The answer to hair algae is phosphate overload, which can be cured with a 50.00 phosphate remover reactor, aka GFO reactor. I use the Phosban reactor. There are several good brands, all using granulated ferrous oxide, all of equal effectiveness. YOu have to change the medium monthly to get effective treatment, and you can stop the monthly changes after you see the algae thin out and go away. You should also be using ro/di water, which is phosphate-free. Spare phosphate arrives with sand and rock, which is the original source. Eventually the rock and sand run out of it, as the Phosban sops it up.