I normally use bleach to chlorinate my pool, but will occasionally use my in-line chlorinator with tri-chlor tabs, only when I am going to be away for a week or more. So my CYA level will go up only when I am away, typically about 7 PPM for each week that I have to use the chlorinator. I don't use algaecide, and don't have any algae in the pool.
My CYA level is currently about 65. I am keeping my minimum FC level at or above the levels shown in the Chlorine/CYA chart, so as my CYA slowly goes up over time, I raise the minimum FC level as well (I use the FAS-DPD test).
I find that using higher FC levels does not require me to use more chlorine since I only have to replace what is lost each day due to the sun. So, it is not more costly to keep my pool at a higher FC level.
The chart says that for CYA=100, the minimum FC level should be 7, and the target FC level should be 12. The shock FC level would be 39, but if I keep on top of things, I shouldn't need to shock it. The footnote in the chart says that CYA levels of 70 or above are not recommended, even though the chart goes all the way up to CYA=100.
So I'm wondering what is really the practical limit to which I can go on my CYA level, before I have to drain the pool? At some point the required FC levels would probably start to become damaging to the equipment, perhaps?