Help...What is this stuff?

The pool company, nor I know what this stuff is. Can someone help me identify it and treat it? It grows in circles and rectangles under the water line. Look under the water in the pictures and you can see it. The fiberglass pool is new and the peagravel hasn't been removed from it yet so don't mind the mess sitting in the bottom of the pool. Thanks for your help. We'd really like to get the mess cleaned up before we winterize the pool for the year.

Thanks
Jon
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If it's growing, it's organic........Clorox is the answer.

Posting a set of test results will probably give a clue or clues to confirm that but my guess is your Chlorine is or has been too low.

Not necessarily Clorox, but any generic laundry bleach is fine. Most of us here use generic Walmart brand which is called "ultra" and is 6% bleach. No scented stuff.