Need a Hanna Phosphate Low Range Checker.
Get a GFO
reactor and run GFO
Use SeaKlear liquid phosphate remover, which can remove all the phosphate in just a couple of days, whereas GFO
can't do that, and would cost you a bit more to run.
Once the phosphate are down, get a Sea Hare, they will take care of that Hair Algae in no time.