Readings took a turn today - FC holds but CYA is gone

[Watermom]

Having a cloudy pool, (plus that CC reading of 1) means that you aren't done yet. A lot of the cloudiness is most likely dead algae, but you need to continue to keep the chlorine high (with bleach, not pucks) a little longer. Have you tried to overnight test? Test your chlorine level at sundown and then within two hours of sunrise the next morning. If you lose more than ppm of chlorine overnight, then you need to maintain the chlorine at shock levels. It is best to add bleach in the evenings rather than in the mornings, by the way, so all of it can go towards sanitizing the pool/killing algae instead of having part of it lost to the sun.

Keep running your pump and filter 24/7 while you are working to clear the pool. Watch your filter pressure and backwash whenever the pressure rises 8-10psi over clean filter pressure.

Also, those pucks are trichlor. You can't shock with trichlor so save them until you are finished clearing the pool and then you can use them. Hope this helps. Glad to see you back around the forum this year!
I can't explain why the CYA dropped from 50 to 0 in that short of a time period. Are you sure it is not a testing error?