I had hair algae really bad - I added rowaphos and scrubbed my rocks with a toothbrush (not as tedious as it sounds) and did a couple of water changes. It's been about a month now and the hair algae isn't growing back. I still have a tuft of it here and there, but its in check.

I also added tons of mexican turbos, cerith, and trochus snails. I think they're helping control any regrowth.