Also, I sometimes run into this problem with hair algae. I have noticed that no critter really likes the long stuff as far as most cleaners go.(sea hair) I have taken a old toothbrush and scrubbed the rock while it was still in the tank. Sometimes this takes a couple of times and some screen cleaning. I have noticed that after a good scrubbing I see more cleaners and fish picking at the area and I have had less return of the hair algae. I have kept tanks with tap water and RO/DI. Also consider how old your lights are. How long between water changes. also, make sure you are not over feeding your tank. Mabe it is still cycling, I did not see how long you had the tank setup for.
Don't give up, it seems to come on fast and go away very, very slowly