Getting back to the CYA and FC... Maybe I missed it, if so, plese ignore me. But if not, then let me try and help you understand this...
You posted this from the manual It says target cya 30-50 and fc 1-3 so I’m confused!
This is where the manufacturers differ from TFP, it's how and for what purpose the FC is used.
Per the CDC, the FC of 1-3 is sufficient to kill bacteria and stinky organisms that can make people sick. And that is true.
But Per TFP, we use Free Chlorine to also control algae, Read that again. TFP uses FC to Also Control Algae! That is the difference!! instead of using expensive and potentially damaging algaecide products sold at pool stores.
So, the correct level of FC in the pool to control algae is a percentage of the CYA. The higher your CYA is, the higher the FC needs to be in order to keep your pool algae free, bacteria free and the water sparkling.
TFP FC recommendation is a percentage of the CYA level. The FC recommendation is 7.5 - 11.5 percent. Because I suck at math, I just use 10% of the CYA level as my FC target. It's well inside the range we need and easy for me to calculate in my head....
FC below 7.5 percent puts you at risk for algae growth.
FC above 11.5 percent is not dangerous at all, far from it. But Its just wasted chlorine and there's no good reason to be wasteful..... It's wasted because at this level, there isn't isn't enough CYA to protect it from burned off by UV from the Sun.
I really hope this helps,
If you still are confused about it, let us know and we'll try and explain it better.