I'm attempting to identify the substance currently residing at the bottom of my diving well. At this point, I've exhausted most of the typical options. Maintaining high levels of chlorine will not reduce, black algae killer has had no effect, and no amount of elbow grease (with a steel wire brush) takes the stuff off the shell.
Does this look like the infamous black algae, or am I looking at a more serious problem?
Thank you for the collective insight!
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