There are a number of ways to rid yourself of hair algae. Depending on your tank and if it is big enough add a quarantined Tang. Ctenochaetus surgeons are the best such as the Kole Tang. There is a reason you had a hair algae outbreak in the first place. There are a few reasons. A new tank, high nutrient levels(i.e nitrates), old bulbs, lack of water changes. You should check your levels and if high, do water changes, adjust feeding amount, improve filtration, remove fish. If you have no photosynthetic inverts then I would completely black out the tank and this will help as well. Also reversing the photo period will help as well. T