What kind of algae is this?

I have been struggling with this for months. I pull it out by the handful every week. It has taken over everything. Can anyone tell me how to get rid of it? It appears white and stringy. When I pull it out it has a rough feel and is green when clumped together. Even though I try to get it all, it still comes back as strong as ever. I have tried lights out, fertilizing, not fertilizing, CO2 fert to 6.0 pH, non-CO2 to 8.o pH. Not sure what else to try. Lighting is 2-4' T5 HO and 2-4' Actinic. Tank is a 90 gal.