[butchblack]

Does look like Spyrogyra, green thread algae. You can physically remove it with a brush, and it will come out in long silky chunk. You can physically remove it or dose with API Algaecide if you don’t mind killing invertebrates. Hard to get rid of as no algae eaters eat it, and thrive in the same conditions as green plant.

FWIW spirogyra is the green thread algae, Spyrogyra was a jazz-fusion band named after the algae.