If you are using a Kit bought from here, then a full tube on a CYA test and you can still see the black dot means you have no measurable CYA.

One of the few ways to lower CYA is to let you pool get the condition you opened to. Go to the Pool store, Lowes, possibly Walmart and buy Stabalizer, this is CYA. Add the recommended amount on the bottle to get you to your preferred level based on the gallons in you pool.

I have a saltwater pool I prefer to run 40-50PPM CYA, others like something closer to 20-30 or 30-40. When I add CYA I put it in an old nylon stocking from the wife and hang it in the skimmer until it disolves. Other wise it just winds up in the filter and you backwash it out if you don't give it a week or so to disolve.

In the meantime you need to get a sustainable FC reading above 10 and keep it there unitl all the algae and cloudiness are gone and if possible a day or 2 beyond. Keeping a minimal Chlorine level of 4FC or less is just inviting the algae to startup again. The DE in the filter is helping you filter out the dead algea that is causing your cloudiness, but you current CL reading with no CYA means you are at risk of a new algea outbreak at any time.