Black dirt on pool wall?

Question

In my public pool for the neighborhood there is black alge-like (as my dad says) dirt on the walls. I realized there keep sgetting more and more. Can this be algea? What is this?

Thanks, a lot!

Answer 1

Yup!

Hard to remove, chlorine resistant!

You're welcome!!

Answer 2

Sounds like black algae to me - you have to get a wire brush and scrap as much off as possible, and then put in special algae chemicals  you can buy from the pool store.