Can you give some details about your set up? Do you have a refugium section in the sump? If so you could possibly add some chaeto to actually compete with the hair algae for the nutrients and hope for it to starve it out. Another hit and miss tactic would be to add a yellow tang. It seems crazy but I've seen these fish destroy hair algae populations. If you have a reactor, you could possibly use a nitrate sponge, bio pellets, GFO
, or phosban. Are you using RODI
water? Have you tested for phosphates? How much are you feeding? What is your flow like in your tank? What kind of lighting do you have? How old are the bulbs?