pH and TA vs. CSI

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Matchless1

Matchless1

0
Jul 10, 2014
298
Baton Rouge, LA
Lately, I seem to be in a constant battle of adding 50 - 65 oz of baking soda every week to keep my TA around 60 (the low end of my target range of 60 - 80). And by the time I add, it's dropped to 45-50. Then, after I add it and get my TA back to 60-65, I find myself adding more acid than when the TA was down around 50. So, I feel like I'm in a constant back and forth between adding baking soda, then adding [more than normal] acid. As the temps drop, I'm going from about 100 oz of acid per week to about 140 oz per week. It's starting to occur to me though that maybe I should really just be focusing on CSI, which considers both pH and TA (as well as CH, CYA and Temp), instead of just keeping the pH between 7.5 - 7.7 and TA between 60 - 80 (and it's never above 65).

For example, today my numbers (before adding acid...I do that in the evening) were: FC: 6.5, pH: 7.9, TA: 60, CH: 275, CYA: 36, Temp:52°F, CSI: -0.19.

But if I were to shoot for a pH of 7.5 and add 28 oz of acid tonight, my CSI would drop to -0.53, which would border on the "Corrosion" warning at -0.6. Also, adding more acid is driving down my TA. Conversely, adding more baking soda is driving up my pH.

I know it doesn't help that I still have a residual Borate level of 30 (I learned the hard way that adding Borates drastically increases acid consumption), so I'm slowly waiting for that to drop to 0 one fine day probably 2 years from now. I also know the colder temps aren't helping right now either.

Anyway, has anyone else experienced similar see-saw effects with pH and TA? Am I wrong to use CSI as my guide for whether or not I truly need to keep my pH and TA between the ranges mentioned above? In other words, I guess what I'm considering is (for my current water temperatures around 52°F) letting the TA hang around 45 - 50 and pH at 8.0 - 8.1, which would put my CSI at -0.25 or -0.19 (similar to above). This would allow less addition of both acid and baking soda (saving $$$ and time), while yielding the same (or more neutral) CSI. Basically, at the end of the day, isn't it all about having a good CSI reading or can high pH and low TA readings on their own cause issues?
 
First, baking soda will not drive up pH. Do you have active water features that are aerating the water?

Try not to fight TA. I keep mine in the 50 - 60 range.

I have to ask, how are you testing to get a specific number like "CYA: 36"?
 
It does seem like you're chasing your tail, huh? Were you having these problems before you added borates? Once borates are added, it does get a bit harder to tweak your pH and TA I've read. That's why we tell folks not to add them until things are already stable.

Are you running your water feature on that rock mountain a lot? That sure will drive up your pH. If so, try to tone that down in the cooler weather to just an hour or so a day (to keep the lines refreshed with chlorine).

A TA of 50 isn't unheard of. Each pool has its own personality and yours may just need to be TA 50 to keep the pH down. Its okay. I'd like to see you stop having to add baking soda so often and see where things level off.

Maddie :flower:
 
tim5055 said:
First, baking soda will not drive up pH. Do you have active water features that are aerating the water?

Try not to fight TA. I keep mine in the 50 - 60 range.

I have to ask, how are you testing to get a specific number like "CYA: 36"?
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YippeeSkippy said:
It does seem like you're chasing your tail, huh? Were you having these problems before you added borates? Once borates are added, it does get a bit harder to tweak your pH and TA I've read. That's why we tell folks not to add them until things are already stable.

Are you running your water feature on that rock mountain a lot? That sure will drive up your pH. If so, try to tone that down in the cooler weather to just an hour or so a day (to keep the lines refreshed with chlorine).

A TA of 50 isn't unheard of. Each pool has its own personality and yours may just need to be TA 50 to keep the pH down. Its okay. I'd like to see you stop having to add baking soda so often and see where things level off.

Maddie :flower:
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Sorry, I guess I meant that adding baking soda increases TA, and it seems to me like a higher TA is causing my same acid additions to have less of a drop in pH than when the TA is lower. Also, the Pool Math calculator does state that an "Other effect" of increasing TA is a [very slight] rise in pH...probably negligible though.

I do have a waterfall and a slide, but this time of year I run them both for literally 1 minute every day just to keep the water in those pipes (as well as the water at the bottom of the falls) from getting stagnant. So, aside from freezing temps when they both kick on for a while (which did happen these past few days), these should not have an effect on pH this time of year.

I added borates after one year, but maybe things weren't really stable then...I thought they were...wish I would've never done it. I thought I researched it enough before adding them. I found all sorts of positives, but I guess I missed the warnings about increased pH. Never again!

I use the thin (dime-sized diameter) graduated cylinder in the TF Test Kit to measure CYA. It's pretty easy to get down to the ones digit.
 
Matchless1 said:
I use the thin (dime-sized diameter) graduated cylinder in the TF Test Kit to measure CYA. It's pretty easy to get down to the ones digit.
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The Taylor cylinders are graduated to a resolution of 10. As the difference between reading is logarithmic, not linear any spot between marked numbers is a guess, meaning half way between 40 and 50 is not 45. Always round up to the next graduated marking.
 
I agree with JamesW and also would not correct to 7.5 when/if it gets to 8.0, but instead just go down to 7.7

Higher TA will cause your pH to rise more quickly, but won't lead to higher acid use. That said, every bit of TA you add has to be offset with acid to maintain a constant level of TA. So any added baking soda, or the TA in your fill water, has a measurable amount of acid needed to offset the added alkalinity. If you're getting more evaporation, you'll see a rise in TA coming from top-up water.

It sounds like you understand CSI well, and yep your instinct is right.
 
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