Ok, let me jump in here. What I'd like to see is you run the FC/CC test with the 25ml sample just once, and see if your CC now tests at <=.2ppm. If it does, then the 10ml <=.5ppm is leading you on a merry chase. Quite frankly, with white cloudy water and a CC of <=.2 and high FC, I'd say don't worry about the CC anymore.

I didn't see if your pool is a sand-filtered, but if it is, tray adding a little DE through the skimmer, just enough to raise the pressure one pound. What you have may be too fine for sand to catch. You could also try a slime bag.

Another tool is the only algaecide we recommend: Polyquat 60%. This can also function as a clarifier since I think you've killed your algae.

FC may well be dropping if you have a lot of sunlight, even with CYA=30-40ppm. I'm not convinced you have any algae left to metabolize. I'm currently boosting my own CYA, aiming for the 60-70 range where I intend to keep it and run higher FC levels.

Carl