My tank was about six months old when I got a bad case of green hair algae. I tried many things to fix it and I finally won. Here is my opinion.
I think live rock 'dies off' after a while after being introduced into the home tank. This in turn releases nutrients into the tank and any hair algae spores come to life.
I didn't have any luck buying specific creatures to consume it. All failed. I tried turbos, emerald crabs and an algea blenny. - no luck.
I managed to control it with the following attack.
Don't over feed. If you use frozen food, rinse it with ro
or let it thaw onto a paper towel.
Days without light
But most of all.... Pull it out! Get as much out as you can. Use a tooth brush. I used an electric toothbrush! Then use a net to capture most of the algae floating round. Take the rocks out if you can and scrub them. I know it sounds extreme but you will do it in the end anyway.
I believe you have to physically remove it to get it out the system. It will just keep feeding itself.
I hope this helps.