Back in mid July I posted the same issue and ultimately feel my filter is at fault and that this is not algae. We all seem to have Hayward sand filters, I don't know of any form of algae that just settles, it either is in suspension or attaches to something.
I know with my filter I can feel a slight suction on the return jet when I backwash and it took 7 days of 24 hour filtering to remove the cloud after spring shock so I'm pretty sure I have a bad spider gasket. Closing for spring I vacuumed to waste to remove the brown wonder and so far, 2 days later, nothing on the bottom. I will continue to check it over the next few weeks and report back.
Can someone siphon some out, put it in a glass and then shock the glass water and see the results? This should determine if it's organic or not.

Wayne