I'm still fighting off a hair algae invasion in a 10g tank. I cut down the light intensity and photoperiod (2 13w CFLs) and have increased fertilizer 25%. Making small moves here I hope.
You might try vacuuming weekly. My hair algae is at the top surface of plants. That makes me think that the light is too high, but I could easily be wrong.
If you haven't already heard this, you can use a toothbrush to remove hair algae by picking it up by twirling the brush.