First you need to clean as much of the hair algae as possible out. This will give your algae eaters a head start, the stuff grows faster than they can eat.
+1 on finding out what is the cause…Phosphates and overfeeding are the common causes.
If you scrub your rock (I had to) do that in saltwater or you will kill even the good critters.
My tank now has a very tiny bit of it around the power heads..it does not last long with the Kole tang, red lipped Blenny and Hippo tang. The Kole and Blenny are what I bought to eat the algae…there are quite a few choices on what to get for an algae eater according to tank size…I have a 90g so the Kole was my choice. The Blenny was overwelmed and needed help.