I saw a large sea hare (Dolabella auricularia) munching on hair algae at The Aquarium Shop on Monday. He may not be a bad one to have if you can safe guard your powerhead.
On the other hand, if your algae is mainly on the glass surface, you might be able to just scrape them off with a razor blade. It is good to have a small tubing (1/4" ID) ready to siphon out loosened hair algae as you go (keep the siphon going but pinch the inlet side closed with your fingers.)
Tomoko