Burn marks on floor

[poolnj]

I just noticed what looks like burn marks on the floor of my pool (vinyl liner). I'm pretty sure they weren't there this morning.When I brush them, nothing happens.

I turned on a Hayward chlorinator this morning with pucks (I usually don't use but wanted to add some CYA). I turned it off now because seems there is something wrong with the valves because my pool got a ton of sand.

Could that have caused this and if so, what is it?

 

[Mdragger88]

That looks like rust.
Perhaps something metal got into the pool?
You can try some crushed up vitamin c in a sock to see if it removes it.

 

[Mdragger88]

Your signature says you have a DE filter. Do you mean de got into the pool?
Have you backwashed recently & replenished de?
Or inspected the grids recently?

 

[JamesW]

Looks like a piece of rusty metal.