[Dearth]

Hair algae is one of those funny algaes that can completely over run your tank then suddenly disappear almost overnight

It is also an algae that self supports itself so it tends to be very difficult to get rid of

You could see if you could borrow a Sea Hare it would make short work of the algae

Tangs will eat it but also from what I understand can be very picky about what they eat

Scrub scrub scrub your rock very labour intensive and can take several weeks of daily scrubbing to make a dent

Fresh water dip your rock but comes at a price of kill off and increased everything

Just some options