It looks like metal stains. I had some ascorbic acid from my metal stain issue earlier this summer, so I put some in a sock and sunk into the deep end. Within a couple of minutes, the area around the sock turned darker brown, and a clean white trail emerged in a line between the sock and the main drain below it. I assume the darker brown was the stains lifting off the bottom. The darker stain did significantly lessen after a few minutes, but I assume that could be the ascorbic acid in the pool. So... do you think I need the full ascorbic acid treatment or should I just try some metal stain remover?