In your first post you said that you had the brownish deposits above the waterline. In areas where it's "caked", can you scrape it off without damaging your liner? If so, I would do that and then try a sponge with a paste of baking soda and water to try to remove any residual. As for the stuff that you saw settling around the bottom of the pool, my bet would be sand that is either blowing into the pool due to a broken or cracked lateral in your sand filter, or dust/pollen that is in your water. I can't think of any kind of algae that would multiply so quickly that you can visually see it increase in a 2 hours period. I would vacuum the brown stuff out to waste, but watch your returns when you turn the pump back on to filter and see if you notice any sand blowing into the pool. If it is algae, then shocking the water will take care of it. However, I don't think that's the problem because if you have enough algae to be that visible all over the pool, 1)you should have some combined chlorine, which you don't, according to your posted numbers, and 2) it should be green, not brown. My bet is on sand.

The brown deposits that you refer to in your last post--are those the sandy looking deposits settling on the bottom, or are those caked deposits elsewhere in the pool? Are they loose where you can disturb them by rubbing with your hand and causing the brown to dispurse, or do they appear to be more like stains?
Is there a source near you for excessive dust/dirt--wells being drilled, new construction, etc? I haven't looked at your profile yet to see what part of the country you're from. Is there a great deal of pollen, maybe?

Make sure that you recheck your pH today--don't know what effect 1.25 pounds of reducer will do to it, but you want it to stay above 7.0, and preferably in the 7.2-7.6 range. If it goes too low, you can use Borax to raise it.

As for the stabilizer, make sure that the amount that you broadcast is swept around regularly and not allowed to sit on your liner--it is acidic and will stain at the least, or possibly damage the liner at the very worst. I personally would backwash the filter, then vacuum the broadcast CYA into the filter and let it disperse from there. 2.5 lbs seems like a lot for an 11K gallon pool, though--you might want to consider just vacuuming it to waste along with the brown stuff and then rechecking a CYA level after the amount in the sock has had time to dissolve (allow 3-4 days after it's dissolved to retest because it often takes several days to show up in your water and it's much easier to add more later if it's low than it is to reduce it if you overshoot. You want to start with about 20 ppm in your pool.)

Finally, what is the source of your fill water? Is it possible that there are metals in the water (iron, copper)? Aside from the brown deposits, what does your water look like? Clear? Cloudy?

Sorry for all the questions, but sometimes it takes some narrowing down in order to zero in on a solution!

Janet