I have a problem with green hair algae on my live rock and don’t know exactly why.
Nusiance algae needs 3 things to live. Food, water and light. You can't remove the water, you can't remove the light (you can turn them off, but when you turn them back on the algae will return), so you must remove the food...which is nitrates. Have you also tested for phosphate?
Are you using 0 nitrate RO
water for water changes?