From Reef Cleaners:
Clean Up Crew- Assorted Hermits, Blue Legs, Florida Ceriths, Chitons, Turbograzers, Sea Hares, Conchs, Emerald Crabs, Urchins and a few others. It is readily accepted by many herbivores, but because it grows quickly it may persist even in a tank with a fair amount of cleaners.
Why it Happened -An excess of available nutrients, particular the majors like phosphates and nitrates. Keep an eye on possible iron and potassium sources which may also help fuel hair algae. Hair algae spores and fragments are so abundant that keeping it out of the tank via quarantine is unlikely to be successful. Your best bet to preventing this algae from taking hold is to maintain a weekly water change regimen, maintain your filtration and perform manual/natural algae removal as it forms. Proper magnesium and alkalinity levels are thought to discourage the growth of many species of GHA.
Personally what worked for me was pulling it off the rocks and 1 dose of algea fix.