The only thing I see in terms of tests is that your FC is 2. With 6000 gallons, one gallon of 6% bleach should raise your FC by 9.5. With a CYA of 30, you need an FC of 15, constantly maintained. That means about 6 quarts of 6% bleach to get you to 15ppm, then 1 quart for every 1.5 ppm below 15ppm, and checking 3x/day.

I haven't seen that you are doing that unless I'm missing something. Once you've done THAT until your FC level holds the clearing should be possible. But if you water isn't blue, you have algae. If your water is blue, just cloudy, it's just stuff that has to be filtered out.

I don't understand your dual filter system. Ben does, but I don't. I would suggest just using the sand filter and cutting out the cart for now. KISS. Meanwhile, another user who is having TERRIBLE metal problems (you don't seem to have that) is using a secondary jury-rigged filter using a sump pump to force water through a five-gallon covered bucket filled with batting and other material to catch any particles. It's pulling a lot of metal out of that pool. I do not know if it will work for YOU, but if you have a sump pump, some hoses and a 5 gal bucket with a tight lid (that Home Depot sells for $3 or $4), you could try it.

Carl

Chlorine is chlorine, whether it comes in bleach bottles or tri-chlor pucks. Sorry if your kids don't "get" that.