If I understand this correctly, we are to subtract 1/3 of the CYA reading in ppm from the TA reading to get 'actual' or 'functional' or adjusted TA.
I had never heard of this rule but now it seems it's everywhere I look. That explains the "adjusted alkalinity" I've seen on water test printouts from the pool stores.
In one of the CYA threads one of the forum gurus (sorry, I cannot find the thread I'm referring to) said that we already take the CYA/TA relationship into account when we make TA recommendations. Am I correct in my understanding then that, when we shoot for a TA of between 80 and 100 in a vinyl pool in which CYA is between 30 and 50, those TA value recommendations are based on the CYA levels?
I understand that alkalinity acts as a buffer for pH, keeping it from fluctuating. The pH readings of my water have been 7.5 all season. I started with a TA = 100 and CYA = ~30 back in May. I'm now at TA = ~85 and CYA = ~50, pH at 7.5. Since there has been no change in the pH in many weeks I had no plans of increasing the alkalinity - until I read about this 1/3 rule. Should I?
Sometimes, I think I'm way better off the less I know