Welcome to TFP!
Adding copper to a pool comes with some unpleasant side effects, sounds like those are just about to start catching up with you. For the extremely limited benefits of copper (your pool may be clear, but since when does clear water mean safe water? Copper offers zero sanitation, only algae prevention) it is highly discouraged here and I personally consider it one of the worst things someone can use in their pool. The sales tactics used by those selling the systems are sickeningly dishonest but very persuasive. I'm not a fan, is what I'm saying.
Anyway, the green backwash is copper, no two ways about it. If it is coming out of solution in the filter then staining is almost a certainty soon. Water replacement is the only guaranteed way to lower copper in pool water, other products are hit-and-miss at best.