You do not show what your TA is. Your CSI should be easy to keep below 0 with that CH.
Are you sure they are black, or really dark blue? Take some and put a drop of acid or vinegar on them. See what happens.
TA is 60.
I gathered some of the “black fleck” and put it on a white dish for contrast. (See new pic) There actually are blue flecks mixed in with the black. When I add vinegar nothing really happens but the vinegar does turn a slight blue hue.
