As mentioned; your pump is way over sized for your application. If it is 220 volt, look for a dual speed motor that runs at 1 horse and 1/6th horse. You should never use the high setting. Be sure you get the correct "Frame" for your application. If your pump is 120 volt, look for a third horse motor or smaller or figure out a way to run 220 out to the pool.

I did not recall seeing if you cleaned the cartridge after a vacuum to see how much of your particulate matter was picked up. With that, as with a sand filter, too much flow could blow debris right back into the pool.

Could the pump be blowing by the filter? Heck, that pump could be blowing your filter to shreds.

And finally, your cartridge may have holes that are not obvious unless there is a close inspection.

As for the overnight dust; very viable and very common no matter where one lives. My pool is in the woods in Central NC and my brother has the same inground pool setup in Whitehall, PA. I actually have much less dirt on the bottom than he but more plant debris and bugs. One benefit I have with my dual speed is that I run it 24/7 all year round on low and only use high to backwash or vacuum to a 200 pound sand filter. The only problem I have seen with this method is a new seal every three years which is a piece of cake to change with my Hayward Super Pump. Well that and no open/close seasons for me either.

Good luck and let us know how you fare with this.