High pH - Normal?

[Kit]

Seems like whenever I check the pH level in my spa each week I notice that the pH level is 8.2 ppm. With a target of 7.4 ppm, I naturally add the appropriate amount of acid. The next time I check the pH it's back up to 8.2 ppm. Is this normal?

I might add: (1) the spa is covered, (2) it is rarely used this time of year, (3) water temp = 57 - 65F. All other chemistry levels are on target.

Thank you kindly.

Kit

 

[JoyfulNoise]

What's your TA?

pH rise is completely dominated by the CO2 outgassing that comes from the aeration in the tub. TA is a direct measure if your carbonate alkalinity. If your TA is too high, pH rise (or acid demand) will always be present.


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[Kit]

What's your TA?

pH rise is completely dominated by the CO2 outgassing that comes from the aeration in the tub. TA is a direct measure if your carbonate alkalinity. If your TA is too high, pH rise (or acid demand) will always be present.


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Matt: TA = 80ppm. And since the spa is rarely used this time of year, the only aeration comes from the daily 2-hour filtration cycle (about 1200 rpms).

Kit

 

[JoyfulNoise]

We typically recommend keeping the hot tub TA down at 50ppm just for this very reason. Even just a few cycles are enough to drive up pH. You can also add 50ppm borates to your spa water to help control pH rise.


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[Kit]

Matt: Does the target TA of 50ppm apply for a 2,360 gallon, in-ground SW spa like mine? If so, is there a preference of either lowering the TA to 50ppm or adding 50ppm of borates to control pH rise? Thank you!

Kit

 

[JoyfulNoise]

You could get a bubble cover for the pool. If you fit it snug to the walls it will arrest most of the CO2 outgassing and hold down the pH rise.

If you pH rise is as fast as you describe (0.5+ pH units in 24 hours), then borates will barely make a dent.

Is this swim spa newly plastered?


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[Kit]

The spa is always covered with an auto cover (which is always in place except when in use). No, the spa was plastered one year ago.

 

[JoyfulNoise]

Try to lower your TA to 60ppm. See what impact that has on your acid demand. The auto cover should be sufficient as they typically ride on the water surface a bit for buoyancy.


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[Kit]

Thank you, Matt. I will give it a try.