Vinyl, SWG. Rails are oxidizing (planning to paint tomorrow), could it be from this? Today, I found this shown in the pic. Specifically, the white line is what I'm asking about, but any advice on removing the stain above it is also appreciated. There was a fine brown line over it, but it easily brushed off. This is ONLY on the side of the pool that gets morning sun if that makes any difference. Also, this is the typical water level line, I've just neglected the pool and found a leak today so it's a few inches low. Advice greatly appreciated! TIA!

PH 7.3
Alk 130