I tried several sea hares before, but to control Bryopsis, not regular hair algae. Either way, they didn't touch it. But they're supposed to be good at removing most algaes.
Now that your nutrient levels are lowered, manual removal would probably be best. I know, it's not fun, but whatever you remove should stay away for good. If it's the really fine hair algae then you can attach an airline siphon to the head of a toothbrush and scrub/siphon it off.
Good Luck!