I included this in the Deep End (mods, feel free to move if appropriate) because I wanted to get into algae behavior.
Does algae go dormant during the winter? How does algae in a pool react to freezing water/freezing temps?
I've the the same issue as a lot of other people have had, and I had it last year as well (before switching to BBB). Sediment collecting in the uneven areas on the bottom of my pool. It also collects along the liner seams. When I touch it, I can't characterize it as slimy or gritty. Depending on the patch I touch, it could be one, the other, or both. It brushes/vacuums up easily, and "poofs" into a cloud of dust. So easily, in fact, that only a strong water current will make it "disappear", only to redeposit a few hours later. I can vacuum the entire pool, but it redeposits within a day. I don't know if it's a true "re"deposit or if it's new material dropping to the bottom.
One of the reasons I'm questioning pollen is that I've had a solar cover on for about 36 hours, and I haven't had any dirt/dust/pollen appear on top of the cover, but the bottom of the pool looks filthy again.
When I opened the pool, my CYA was about 65-70, so my shock level was 19. For about 4-5 days I never let the pool get below 22, and it spend most of the time between 24 and 26. I passed the OCLT and let it come down to maintenance range. The water temperature during all of this was in the mid 60s. My pool has never been clearer than it is right now.
Back to my original question about dormancy. I have white wedding cake style steps that I took out of the pool over the winter and just let them sit on the deck. Here's my theory: The algae has all along been living in or on the steps. Algae didn't die during the winter, only went dormant. During the shock process, I missed brushing it, and it was never completely eliminated. Now that the water is warming up, it is trying to multiply in that bad circulation area. As soon as it tries to live in my properly chlorinated water, it dies, settling to the bottom. The "original" colony is still holding on because it's stuck somewhere where my chlorine doses won't get to it (until it grows).