Grey jelly with threads

[Wombat2]

Hi first post here. My pool has issues off and on that I can usually handle but lately something new has cropped up. I am getting an off white/grey jelly like substance collecting on the wall in a band at the water line. It's about 1/4" to 1/2"" wide and close examination you can see fine black threads through it.

First up I thought it was just scum from a big clean up of algae growing on the wall after winter which has taken a while to get on top of but the pool is pretty well good now but the jelly keeps collecting .

Any ideas what it is and how to get rid of it ?

David L