Thanks for the reply I will answer as best as I can.

I don't use the raw well water to make any adds,have an iron remover on the water system if I need to add. We are in Ohio and it seems we get enough rain to keep the pool level up. My winter cover is the safety type that lets water in.Usually have to put water out several times before pool open.
The chlorinator feeds after the heater.Sounds like I need to use only bleach.

The ascorbic acid removed the stain pretty quick.
I don't have a way to test for iron or copper .
Had it tested at two different stores ,one said the copper was 5, the other didn't list any. They may not have tested for it.
I beleived the stain was from iron when first detected and didn't put much trust in the test that said it was copper.
As an added note ,we live within a 1/2 mile of an operating steel mill.Though they have a dust collector system I'm sure we receive some pollution.We see the brown stain on some of our vinyl siding. Idea!! I never tried to take the stain off with Ascorbic acid. I will try it .
Looks like I need a test kit for metals? Need some advice on that.
Finally I would like to avoid a complete drain at this time. We had planned to replace our 18 year old liner in the fall.