If you can solve the problem without the use of chemicals, I would take that route.
As others have mentioned, low phosphate = GSA. I am now putting over ~7ppm phosphate into my display tank per week (a lil over 2ppm every other day). If I miss even one day, sport algae will show up before my next dosing.
As far as hair algae goes, I recommend as much manual removal as you can as well as fixing the nutrient situation. I have found that using airline tubing allows a longer duration of sucking up all the hair algae. Keep with it and good luck!