Have you tested your water for PO4
What are your other water parameters? Describe your tank set up,size, filtration, lighting, inhabitants, feeding schedule and foods fed, etc.
Reduce your lighting period to only a couple of hours a day or possibly go dark for a week.
Reduce feeding to once every 2-3 days.
Get a RO
filter and then use only RO
water for water changes.
Start with 10-20% changes every other day for a couple of weeks.
Get some Turbo grazer snails and place them on a rock covered with the hair algae.
It can be done but it takes time. I won my battle after changing my PC
bulbs, getting some turbo grazers and a lawmower blenny, reduced my lighting period and reduced feedings. Others have done all of that and are still battling it a bit.