Next'... Can you post YOUR testing? All of it and then we will let you have it.. Don't just tease with terms like pH stubbornly low or CYA stubbornly high!.. I'm not sure what number that is! Anthropomorphism doesn't work on this one. When you say, FC is a hot 23.5! My mind drifts to HOT rods, HOT babes, HOT cakes...
So .. these are the numbers you did say
FC 23.5... since I don't know what your CYA is I can't say whether that is high or low... follow this chart
FC/CYA Levels..
If you need to drop your FC you can do the following in no particular order
1) Pee in it, that will consume chlorine
2) Dilute it with water
3) Wait for the sun to degrade it at a rate of 4-5 ppm per day if you are not adding any chlorine sources...
Now post up YOUR numbers and don't be stubborn about it