if its staining you can try jacks magic stain identifying kit. They have some good products to take care of most problems.

Over 800? Are you doing anything to deal with that? I think "normal" is between 200 & 250. There is a good chance that it is scale. And at that level your pipes and equipment are probably scaling, too. Do you have a white ring at your tile line? If it is calcium scale I believe the general answer is an acid wash. But the problem will continue to come back if you don't deal with the water.

We were going to drain it and refill to get rid of the calcium, but if the pool has to be drained for acid wash or sanding or whatever, we wanted to only do it once. But like I said, I can't get the original plasterer to even look at it. Is there any chance he screwed up the install and the calcium is leaching out of the plaster or something? If you look at the picture, the light brown color on the top step was the original color. The darker color doesn't look like staining, it looks as if the color was only on the surface, (like paint almost), and is wearing off.

Do you have a high water table by any chance? Are the stains "streaky" along the walls of the pool?

The pool company finally agreed to send guy out. He took a diamond abrasive pad and rubbed it on a discolored area, and.... It took the green off and exposed the normal color underneath. He said it's metals and minerals in the water staining the surface and can be removed by draining the pool and using diamond abrasive wheels to take off the stain. Normal cost is $1200, he said he might get it down to $850. Does this sound right? Is there any other method? Is the price reasonable?
Thanks for any information...!

More concerning, where did the metal come from? Did you fill with well water? Do you check your pool chemistry regularly?

You can google "ascorbic acid metal treatment" and come up with instructions for using that. But if you don't find out where the metal came from, it will happen again.

It's city water. We have copper pipes from main drain and skimmer to the pump. I've used algaecide in the past and supposedly it contained copper. Actually not sure it's copper stain, and I don't trust my pool company entirely - so..... I ordered Jack's Stain ID kit.
I tried the "rub a vitamin C tablet on the stain" and it didn't do anything.
Honestly, i don't know whether to follow my pool guys advice and have him grind the stains off because it seems I'll be losing plaster thickness. Would an acid wash be better?