What is the pH level?

Low pH can keep copper in solution, in spite of high copper levels. But, I've occasionally seen low pH with high alkalinity occur as a possible cause of greenish clear water.

Also, it would be good to test your sand filter. If you really have a 75 gpm pump, you may have blown a lot of your filter's sand out, during backwashes. One way to check is add a quart or so of DE powder to the skimmer with the pump running. If it blows back into the pool, via the returns . . . your filter needs service, and your pump may need downsizing. If it STAYS in the filter, it will help remove algae particles, and may help remove copper or iron, but will cause the filter to stop up more quickly.