Just a thought, as you've been working hard at this since around May 21 or so, and the water is still far from clear... Given the inadequacy of the stock Intex filters, you may want to consider just dumping the water, cleaning the empty pool as much as you can, and refilling. I know that may be an unwelcome suggestion after all the work you've put in, but the filtration systems sold with these pools just make it very very difficult to recover from a situation like this.
I don't remember from reading through your thread, but have you tried turning the pump off, letting the debris settle, and then vacuuming to waste? The way to do this with this type of pool is to get a siphon started, and then vacuum the debris overboard. If you haven't yet tried this, it's a more conservative approach than dumping all of the water, and definitely worth a try.
All my direct pool experience is with the equipment mentioned in my signature (and a previous 1000 gal pool with even more woefully inadequate filtration), so my suggestions come from personal experience.