UV. Suck as much as you can every day or other day. I also used a hob filter and blew rocks to get remnants. Take out filter and rinse. Rinse UV pump and filter frequently.
You need to remove as much as possible. UV keeps it from reproducing but does not kill it. You can do it takes a little time.
You want to encourage other algae, gasp hair algae, or diatoms while pulling as mush of this **** out as you can. Feed your fish, they will appreciate it.
I beat in in 6 weeks. You need to get something to out compete it.