Grayish creeping stains?

[jeffdw]

So last year my salt chlorine generator keep giving me a low salt warning every week or so, we did have a lot of rain and humidity. But like dumb A, I just keep adding salt. Anyway, finally have checking my salt was around 6000 ppm, and my cell apparently had died.
Shortly after correcting all that, I started noticing these grayish streaking stains on my plaster pool mostly on the bottom shallow end of the pool and the same color stains on my steps more in a splatter pattern. They are not rough to the touch, won’t come off with chlorine tablet or vitamin C. Looks like pitted dirt but won’t come off.
I have read a ton on the effects of salt and high TDS on plaster, but with so many theories, products, treatment, etc. I'm not sure what to do about it or if it is related or not.
Can anyone identify these from the pic below or have theory or treatment that has worked for them, etc. The stains are surrounding the center diamond title.

I don’t have a good reading on pool chemistry at this time, as I just opened the pool. Trying not to adjust to much at this point, until I see if I have lower, raise anything to help with treatment.
The stains did not seem to get any worse from sitting over winter, pretty much the same from when I closed.

 

[duraleigh]

No pic?

 

[jeffdw]

I attached and it says it is attached but won't post or let me delete it to repost....????

 

[onBalance]

It appears from the above picture, that there is a slight turquoise color on other areas of the plaster, which is an indication of copper in the water.
Therefore, the gray/blackish stains could be from more severe "copper oxide" staining.
But it could also be calcium scale deposits that have turned grey over time.
I think sanding that area with 100 grit wet-or-dry sandpaper would remove those stains.
I doubt the high salt content is the reason for the stains.