Keep in mind much of this is majorly “over-simplified.”
Almost all states acknowledge part of the FC/CYA ratio, the part that chlorine becomes “less effective” as CYA increases.
Almost all states ignore the other part, the part that acknowledges that this can be overcame by a higher FC level.
Many states and cities look at this with the mindset that CYA’s sole job is to protect against the sun, so indoor pools don’t need CYA.
A few states/cities took this further and used a paint roller when making the rules. A handful banned it for outdoor pools as well.
I suspect you’ll find that regulations are often aimed at safety and not as much practicality/cost. Often they’ll be over safe, and for good reasons. It’s almost always able to be overcome……but it’s gonna be expensive. As an example, you’ll be able to keep the pool safe/clear at 4ppm chlorine. To do so you’re gonna use a lower CYA level and a very rapid turnover rate. You’re going to use slow trickles of chlorine, most likely liquid, any time the pool is in use. You’re going to keep the pH lower than we’d suggest as the chlorine will be slightly “more effective” than a higher pH.
