Above the water line, covering a ring around my above ground pool liner is this strange black mould. It was there last summer but before I set the pool up in a few weeks time I wanted to see if I can get rid of it. It doesn't rub off and in fact you can't feel it which got me thinking it might be coming from behind the liner if that's possible.
I've attached a picture so you can see what I mean. I'd love some advice on how to clear it please.
Thanks in advance