Removing copper stains is not an easy process. Especially since you say it is above the water line. I can’t see it in the picture. I suggest you consider it a piece of jewelry on your liner for the time being.
For pool closings we only recommend using Polyquat 60 algaecide which does not contain copper.
Sand in filters rarely needs to be replaced. How old is the sand? You can deep clean a sand filter.
www.troublefreepool.com
Your phosphates should be dumped with the copper water draining. And 2000 ppm of phosphates is not very high.