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The ONLY problems that I have with your method and this might come from my ignorance is that your method doesn't necessarily work for everybody. I've seen posts where people have high TA and low PH - if they drop the TA by using acid then PH will drop as well. And my pool water has been at 95º, a high TA but the PH stayed the same.
I stopped posting/viewing poolsolutions a few years ago. I do pop in from time to time but a lot of what is being said now on other websites came from that website. Maybe the info out of it has evolved through the years and I remained stagnant in my knowledge, chemgeek wasn't around that website when I was active there. I don't doubt what you say but it doesn't seem to jive with what used to be said on the poolsolutions website or what professionals say. Maybe spa water is different than pool water and it does seem to act differently at times for me.
I guess it might be time for more internet water chemistry classes!
I seriously only add dichlor for atleast a month after a refill.
The consumption of chlorine is acidic so even though Dichlor is initially nearly pH neutral upon addition, when the chlorine gets used up this is the same as if you added acid to the water. [glow] In 350 gallons, the addition AND subsequent consumption of 4 ppm FC from Dichlor is identical to 1.2 teaspoons of dry acid in terms of the effect on pH if there were no outgassing.[/glow]If you wanted your pH to be more stable in your situation using Dichlor, you could have the TA be even higher. The pH rise from outgassing would then balance the pH drop from the Dichlor addition and consumption. Over time, the TA would drop and you'd need to add more, but by then some of the TA measurement will be CYA (about 1/3rd, at pH 7.5) built up from the Dichlor and the CYA does not outgas. However, you already have fairly high CH so you wouldn't want the TA to get much above 110 ppm anyway in order to prevent scaling.Richard