black lines inside skimmer

[Booter]

I have a 16 X 28 above ground pool that I opened one month ago. Nobody has swam in it yet. Inside the skimmer at the water line I'm getting a few black lines that feel a little like grease. Do you know what it is or what causes it?

[PoolDoc]

No idea.

There are all sorts of surface debris that can end up on a pool, ranging from a new-ish liner that is 'leaking' plasticizer (the chems added to PVC to make it flexible), to damage from low pH, to blown in smoke or debris from trees.

Even if I'd been hanging around your pool, I might not know what was causing it.

Sorry. Baking soda on a wet towel will clean up many types of water line dirt, and won't mess up your pool chemistry!

[JimK]

I’ve seen that in our pool before, though it’s usually after someone with lots of sunscreen on has been in the pool. My guess is the reaction with chlorine causes it.