I don't know enough about your pool to even guess what the spots might be.
Black algae is a possibility. If you swim down, scrape a bit off and get it under your fingernail, come up and smear it on a white card . . . if you get a bluish-green smear, it's black algae.
Ben
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+ It's much easier to answer your questions, when we have the details about your pool in one place. We often 'waste' the first few posts back and forth collecting information. So, please complete our new Pool Chart form -- it takes about 30 seconds, but will save much more than that.Pool Chart Entry Form
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