Copper Test Kit to test for Copper Ions in the treated water.
When you test the water, it is recommended to test on a white background, if not it is hard to tell the color change. It is easier to see the slight coloration looking at the vial from the top (bird's eye view).
One way to ensure the solution is 100% working is to take the little vial, put two drops or the H2O ResQ solution in it, and the add 3 drops of the Copper Reagent. The water will turn turn yellow.