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I used Concrobium on the CMU walls of my basement, after powerwashing (yes, I powerwashed indoors, and yes that was a mess). Surprisingly, it didn't cause the black stuff to fade. It did, apparently, either kill or seal it, because after that I painted (first with Drylok, then with 2 coats of typical wall paint), and it looked good for at least a year after that (I've since sold the house).

However, OP wants to get rid of the black stuff, so Concrobium would be part of a too-long process. Maybe one of the other mildewcides might work.
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