I am pretty confident I am seeing velvet. On some zebrasoma tangs the parasites look "black" just before or just after they insert which can look like black ich which I think I've seen. I would continue course with copper if I was you. I would stop testing with color tests if you can, but if you MUST use cupramine, use the seachem test kit. Shoot for .5-.55PPM. It's so hard to tell where you are, which is unfortunate because IME cupramine doesn't work below .45PPM.
Doing 100% WC and switching to Copper Power would be more beneficial. Copper Safe is another chelated copper but they have some Quality Control issues with potency (don't follow instructions, dose and test to know how much more to add). You'll want chelated copper at 1.75PPM (with hanna checker) or 2.0-2.25PPM (with color test kits such as your API) -- just because they cannot easily be read and you want to ensure you're therapeutic for the entire duration.