I have a bit of hair algae myself, but it's receding. It's literally a war, and you have to hit the stuff on multiple fronts.
1. The hair algae will spread to other rocks if it has enough light and nutrients.
2. I did the most damage to my hair algae with a two-day "lights out". I shut the lights off and covered the tank with a blanket for two days. I cut my photoperiod down to 8 hours per day, and only 6 hours of full halides total with a long dawn/dusk effect. (Light)
3. I also run a phosban reactor with GFO media to remove phosphates from the water, algae needs it to grow. (Nutrients)
4. I cut back on the overfeeding, and stepped up the water changes to every week to reduce nitrates. (Nutrients)
5. I've hit the worst patches of hair algae with a toothbrush. A little kalk powder in the hard-to-reach places works wonders. (Manual removal/Export).
6. Adding another light over my refugium allowed the caulerpa down there to grow bigger and remove even more nutrients from the water. Caulerpa also releases a toxin (caulerpenyne) that stunts the growth of other algae. (Competition)