I can't imagine any real amount of copper would show up to generate that amount of response.Yup - in a moment of absent-mindedness, I accidentally used by Fish QT heater inside of my Coral QT. The fish QT had Cupramine in it. I immediately washed all my hardware with baking soda and vinegar but I just got copper readings from my coral tank. Fortunately there's only zoas and mushrooms but I just overnight shipped carbon, polyfilter, and cuprisorb to my house. About to do a 90% water change as well.
I can't believe I swapped my hardware. This is a huge, avoidable headache.
Maybe a little polyfiler or carbon.
What kind of test kit?
How many gallons is the frag tank?