The levels are in what is called a "Best Guess" table. If you haven't had problems, then you don't have a problem.

These are empirically determined values that seem to be most effective. It's not guaranteed that you will get algae with FC=2 at CYA=35. If you don't see CC turning up, and you don't get algae then you are probably fine.

People, however, frequently come to our guidelines because they DO have a problem and their old methods or pool store or pool service advice just doesn't work.

Again, it's a "Best Guess".