Wy Renegade
Aquarium Advice Addict
Unless you have corals this is useless. The main reason for hair algae grown is water quality. There are phosphates that are present that the algae are consuming. Remove as much algae and do a big wc. The wc will remove the phosphates in the water and removing the algae will stop it from eating existing phosphates in the water. Keep this up weeks and they should eventually disappear.
True, however since the OP has corals in his tank and has stated that s/he can't remove all the rocks, this is hardly a useless step. Cutting back on lighting or shutting it off completely and covering the tank with a dark cloth during the day will eliminate the light the algae needs to grow and kill off the algae you can't scrub/remove.
Never scrub algae covered rocks in the tank, that simply spreads the algae in the tank. Once you've removed all the algae you can, as was stated you need to do a water change immediately to eliminate as many of the excess nutrients as possible. Adding a GFO, algae turf scrubber, phosban, or chemipure will all help with removing those excess nutrients as well, as will a refugium filled with macroalgae if/when you harvest the algae.