Salt water, pH, and the rational for keeping pH between 7.6 and 7.8

[bmpardo]

Hi, everyone.

I've been following the Trouble Free Pool philosophy since we renovated our pool in April 2024. Indeed, our pool has been trouble free, but I'm still wondering why the pH wants to settle around 8.0 or 8.1.

We re-plastered our 12,500 G salt water pool 10 month ago with a Pebble-Tec like product. Various sources on the TFP website indicate that the ideal pH range is 7.6 to 7.8 for a plaster and salt water pool like mine. In order to maintain this level, I need to add about 4 oz of muriatic acid every other day. I was under the impression that it was the new plaster that was driving the pH up, but that this effect would diminish over time. After 10 months, I don't really see much change.

I'm writing because I hired a local pool company to help me with an equipment issue. The technician struck me as experienced and knowledgeable, so I asked him about my pH levels. He said that salt water pools typically have higher pH levels and that I should try to maintain a pH of 8.0 or less and only add acid if the pH rises to 8.1 or more.

How does this community react to my technician's statement? I have a feeling that most people will strongly advise that I stick with TFP's recommendation: 7.6 to 7.8. That's fine, but I would respond with the following question: During the winter months, when no one swims, the water temperature is about 55 degrees. At a certain chemistry level, if the pH is 8.1, my CSI is -0.070. If I drop the pH to 7.7, the CSI drops to -0.450. During the summer, the water temperature is about 80 degrees. A pH of 8.1 yields a CSI of 0.160 and a pH of 7.7 yields a CSI of -0.220. So why am I constantly adding acid to fight rising pH levels when higher pH levels seem to be desirable?

Thanks for your help on this.

bP

Cl 4.5
cc 0.0
pH 8.1
TA 65
CYA 70
CH 400
Salt 2800 (I know this is low, but the SWG isn't creating Cl right now)
CSI -0.050

 

[JamesW]

He said that salt water pools typically have higher pH levels and that I should try to maintain a pH of 8.0 or less and only add acid if the pH rises to 8.1 or more.

I would agree with this as long as you can maintain a good CSI.

 

[sande005]

You may find this thread that popped up under "recents" today of interest:
New plaster pool trying to dial in pH

 

[JamesW]

 

[mknauss]

What is your fill water TA? I suspect your pH rises when you add fill water.
As JamesW says, keep pH at 8 if that works. Most people overstate the pH level. A pH at 8 or above the test sample would be purple.

 

[YippeeSkippy]

Just a TIP:
Being in California IF down the road your calcium level starts to rise on the high side due to hard water and evaporation, one way to help avoid scale is to run your pH on the lower end of acceptable.

 

[ajw22]

Various sources on the TFP website indicate that the ideal pH range is 7.6 to 7.8 for a plaster and salt water pool like mine.

Anywhere is from 7.2 to 8.0 is equally good.

Hitting ideal should not be your objective.

 

[JamesW]

If you want to operate at high pH, consider getting a pH meter to verify as the color test tops out and becomes less reliable.

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[ajw22]

If you want to operate at high pH, consider getting a pH meter …

and calibrating solutions.

 

[JamesW]

The color test is still valid, but most people overestimate the color because they don't focus on hue.

A meter will help calibrate your perception of the color vs. the real pH.

Once your color perception is calibrated, you can mostly use the drop test with only periodic confirmation by the meter.

 

[ajw22]

Once your color perception is calibrated, you can mostly use the drop test with only periodic confirmation by the meter.

All the more reason to use fresh calibrating solutions to calibrate an infrequently used pH meter.

 

[bmpardo]

Good morning, everyone.

Thanks for such a strong response to my post. I really appreciate the willingness of this community to share their expertise and experiences. Let me summarize all your replies here for my benefit as well as for the benefit of a future reader.

The consensus seems to be that salt water pools may have a pH that naturally wants to balance at 8.0. And so long as the CSI is well-controlled, there’s no reason to fight for a slightly lower pH. After all, a pH of 8.0 is perfectly acceptable in the TFP methodology. While a pH of 7.6 or 7.8 may be considered “ideal”, it’s not worth stressing over. If one has decided to operate a pool at a higher pH, a pH meter may be useful in verifying the results of the color test as the color test can be difficult to interpret at higher levels. However, one should make sure the pH meter is calibrated.

It was also stated via a link to a different thread that new plaster may cause pH to rise higher for 6-18 months after construction.

Regarding question about the TA of my fill water, it’s about 20.

Thanks again for all the help.

bP