I'm having a hard time with CYA. I understand the basics; it's sunscreen for your FC so it doesn't burn off so quickly. What I don't get is why more is not better.
If CYA protects FC like sunscreen does, then ff you have a higher CYA, then FC burns off more slowly, leaving the FC in the pool to fight organic matter. Sure, you would need more chlorine to make it effective, but once you got to the higher level, you wouldn't need to add as much daily as it wouldn't burn off.
So if my CYA is 40 and I lose 3ppm to sunlight per day, I need to add 3ppm each day to get it back to 5. If my CYA is 100 and I only lose .5ppm to sunlight, then I only need to add .5ppm each day to get 12. Sure I used more bleach to get it up to 12 initially, but now I only add .5 every day to keep it there.
I'm sure this isn't how it works, but I can't get my brain around why not. Can someone explain better how CYA works?