Depending on tank size and how much hair algae you're struggling with, you may want to try American-Flag Fish (sometimes sold as Florida Flagfish). In my experience, they eat hair algae like there is no tomorrow. If you have plants in your tank, they make take some nips at those as well if they're not well fed.
I had a horrible hair algae outbreak in a 29 and 8 of them ate it up in about 10 days. After the algae is gone, you can feed them flakes and I give them about a quarter sheet of nori as well.