?

[Qbmafia444]

can any identify that black stringy stuff

 

[saltyfilmfolks]

Quite likely a cyano, also possibly a dino.
I'd bet cyano.
Blow it off , stir it a bit and maybe look at some bottled bacteria

 

[Ghostcat]

If it is persistent I would look into chemiclean, I've used it and it produced great results

 

[Kamden Uelton]

Black Cyanobacteria.