Can someone tell me what this scary junk is?

[Joeknowskinda]

The brown/red thing is protruding about 3/4 inch from the side

 

[kimkats]

OH MY! I have not seen that one before!!! Have you felt it?

I would get a vinyl patch kit just in case then see if you take it off without hurting the liner. I want to see it when you get it off.

Can you rub the dark stains off?

 

[RDspaguy]

I am pretty sure that is a plaster pool, and I suspect you are going to find a crack under it.

 

[kimkats]

I was going to "argue" with you but when I went back and looked at the wall and see why you say it is a plaster pool. I was looking more at the upper part that is what made me think it was liner...................plaster crack makes a LOT more sense!!! Good call!

 

[JamesW]

It's probably rust from rebar or steel wire below the surface. You can scrape it off.

Try a magnet on the area to detect metal below the surface.

You're going to need to cut out the plaster and steel near the surface and patch with some new plaster.

 

[JamesW]

What is this Black Spot

It doesn’t respond to any sort of bleach or algae killer.

www.troublefreepool.com

 

[Joeknowskinda]

OH MY! I have not seen that one before!!! Have you felt it?

I would get a vinyl patch kit just in case then see if you take it off without hurting the liner. I want to see it when you get it off.

Can you rub the dark stains off?

It just becomes dust when you try to touch it. I am pretty sure they are right that it is rust coming from rebar in the plaster