I've noticed on the FC/CYA charts there is a "rule" saying the free chlorine level needs to be at a minimum of 7.5% of the CYA...
Simply out of curiosity, where does this 7.5% come from, just real world experience, or is there some kind of documentation?
I've also noticed that some very large pool stores disregard this when they claim chlorine needs to only be between 2 and 4 ppm, yet they also set their CYA range from 40-100 ppm.
I would think such a fundamental flaw would have been noticed after being in business for decades...
Anyway, If i had hard evidence, I would be interested in writing these stores to point out their somewhat flawed system.
Simply out of curiosity, where does this 7.5% come from, just real world experience, or is there some kind of documentation?
I've also noticed that some very large pool stores disregard this when they claim chlorine needs to only be between 2 and 4 ppm, yet they also set their CYA range from 40-100 ppm.
I would think such a fundamental flaw would have been noticed after being in business for decades...
Anyway, If i had hard evidence, I would be interested in writing these stores to point out their somewhat flawed system.