I am not an expert on metals in pools but I do have bit of a chemistry background. Your stains look more like iron than copper based on the color. Copper strains are usually blue to black. I am sure your water tests positive for copper unless you have drained and acid washed your pool you probably have a coating of copper deposited in your pool from your ionizer. Could your fill water have a high iron content? I have read posts on here on using ascorbic acid (vitamin c) to remove the stains and I know that many of the commercial stain removing products the pool stores sell are just ascorbic acid. Try taking a vitamin C tablet and holding it on the stain and see if the stain goes away. If it does then you know what you need to treat the stain. A sequestering/chelating agent usually will not remove a metal deposit. It only ties up metal ions in the water so they do not percipitate out as a stain.
Hope I've been of some help.
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