AG Vinyl stains from swampy water... need suggestions.

OK,

I've recently opened an 24' AG pool. The pool has not been opened in 2 years. We purchased the house last year but chose not to open the pool. Over the winter the cover caved in and in went the leaves.

Upon opening, the water was black and smelled. My wife and I first thought of draining the water so in went the sump. Then after some research we decided not to because of possible liner failure and that all the junk was still in the pool anyways. By this time, we had emptied abotu 6 inches of water before we started to fill it up. During the fill we through in 3 lbs of shocks and started hauling up leaves.

Anyways, 2 weeks later the water is clear and the test results looking good. Thank to this forum!!

But, here's my problem... The 6 inches of water we drained has left a stain. The stain is prominently bad on the 6 inches. The bottom is very clean and the rest of the sides are acceptable.

The 6 inch band will not scrub off completely. I've scrubbed with a scrubby from the pool store but only 75% lifts off. Any suggestions? I'm going to try the PH minus in a sock but I don't think it's metal because only the band where we emptied some of the dirty water shows up.

Thanks for any help.