Liner is stained

[Gov]

My pool is only one year old!!!
It is above the ground Doughboy.
I have a grayish ring all around my pool at the water level.
It started to developed last year.
Before I filled it up when I opened it last week, I tried scrubbing it with a mild detergent & a scrub brush.
It didn't help.
Any suggestions on what caused this & how to get rid of the ring?
Thanks!!

[Helper]

It soulds like a oil build up,suntan oils and body oils buildup at water level,your local pool store will have a scrub paste that will make it look like new with a littl elbow greese