I discovered the awesomest natural control for hair algae...red leg hermit crabs. I AM ABSOLUTELY positive they eat green fuzzy hair algae, because I stuck one in my nano which had it, and a day later it was nearly gone. Since he is in the nano, I got to watch him up close...his little pincher claws would grab and rip the hair algae off the rocks and he would eat it...crawling along, until the rock was clean. I wondered why when I moved some Live rock from my main display, it started growing hair algae in my nano when I have never had hair algae in the display!
Now I know why, the red leg hermits in my display are always on the rocks picking and eating, never allowing it to grow. THe hermits love it. You have to get the "mexican red leg hermits". Not blue legs, not scarlets, because I can't guarantee those kinds will work the same. TRY IT!