I have not been able to figure out what these spots are. They are all in pits in the plaster near the water line. Didn't react to vitamin C or my SLAMing over the last few days. I have rubbed trichlor on it in the past and nothing seemed to change. The spots feel slightly smoother than the plaster but not by a whole lot. They all look and feel about the same. I would wait til I am done SLAMing my black algae away but what steps for identification should I do next?