What’s driving my pH to rise so quickly?

[Stoopalini]

See my PoolMath logs for details.

I’ve settled into a routine where I test every Saturday, and notice my pH is always up around 8.1 or so. If the TA is 70 or more, I typically dose enough MA to drop the pH to 7.2 and lower the TA as well. If the TA is less than 60, then I typically dose enough MA to drop the pH to 7.5 or so.

This week, I decided to monitor the pH closely, to see how quickly it’s rising, and it appears to be doing so very quickly.

24hrs ago, it was 7.88 with a TA of 80. I dosed 14oz of MA and that lowered it to 7.54.

Today (24hrs later) the pH is back to 7.8 with a TA of 70.

I tested my fill water as well, which is TA of 140 and pH of 7.36.

The plaster is just now one year old.

I do notice bubbles in my pump basket, which I think is a result of a small suction side leak somewhere. The PB hasn’t figured it out yet, but I wonder if it could be generating enough aeration to impact the pH? Seems to be reaching to me, but worth mentioning.

I also have a waterfall I run on a schedule for 20mins every day. Both to circulate the water in the lines and the basin, but also because my wife loves it so much. Based on the YouTube stream TFP did on pH, I assume this wouldn’t be enough to account for the pH rising so quickly.

So is this rate of pH rise typical for my situation, or should I be looking to address it?

I’m considering adding 50ppm Borates to try and help, but if it doesn’t, then I’ll just be left with having to add even more MA at each dose to result in the same pH adjustment.

 

[mknauss]

With your fill water, your TA is being raised when you add it due to evaporation. That pushes the pH up. So your acid is used to reduce the TA via reducing the pH.

Borates will slow that down. You might go to 10-14 days between adding acid. Overall the same amount of acid will be needed.

 

[Stoopalini]

Thanks Marty.

Even with the overall TA staying 80 or less, you’re saying the 140 TA water coming in has is enough to raise the pH so quickly?

over the past 24hrs, it rose 0.25 pH points. I may have had 2” or so of evaporation during that time. If my math is right, with a 469ft perimeter, that would be just around 50 gallons.

Would 50 gallons of 140TA water be enough to raise the pH of 14k gallons of 70TA water by 0.25?

 

[mknauss]

2" is more than 50 gallons ---------

You could work to lower your TA further and that might slow it down. I just add acid twice a week. My fill water has the same TA, and add about 70 gallons per day of it to my 6000 gallon pool.

 

[Stoopalini]

Sorry, I meant 469 sq/ft surface area, not perimeter.

469 x 12 = 5628 sq/in.
5628 x 2 = 11256 cu/in.
11256 cu/in = 48.7 gallons

I've had my TA down to 60 for a while, then went on vacation where it rose up to 80. Dosing every weekend, and using enough MA to drop the pH to 7.2, is typically enough to keep the TA down around 60 - 70 or so since the pH settles around 8.1.

Maybe it's time to get an IntellipH, or similar MA automated dosing setup.

 

[Stoopalini]

Hmm, we had enough rain today to raise the water level up a couple of inches above the auto level setting.

So maybe I’ll adjust pH now, turn the autofill off for the next 24 hours, and see what it tests tomorrow with no make up water coming in.

 

[mknauss]

Check your math. I believe your pool is closer to 300 gallons per inch of surface depth.

 

[IceShadow]

You have to multiply by 144 to convert sqft to sqin

 

[Stoopalini]

Of course .... 144, not 12 .... So 585 gallons for 2in, which makes a whole lot more sense.

I just dosed MA to drop the pH down to 7.5, and tuned the autofill off. I’ll see what it does over the 24hr period.

 

[Stoopalini]

So last night, I turned the auto fill off, and had a pH of 7.47. Tonight, 24 hours later, the pH is 7.69. Seems pretty much the same as when the auto fill was on. 0.22 rise in 24hrs with the auto fill off, vs. 0.25 rise in 24hrs with it on.

I'm measuring with my 3-point calibrated Apera PH60 meter.

Is this to be expected, and I should consider it normal ... or should I be looking for something causing this to happen?

 

[Stoopalini]

I just took another pH and TA reading now, and it's gone up another 0.10 pH points compared to last night's reading.
So it appears to be tracking roughly 0.10 increase every 12 hours, and this is with the auto-fill turned off. TA is still holding 70.

8/2 8:50 PM -- 7.47
8/3 9:47 AM -- 7.61
8/3 9:55 PM -- 7.69
8/4 10:16 AM -- 7.79

Would this just be due to the natural process of CO2 of the water moving toward equilibrium with the air above the water?

I realize the SWCG process can raise the pH, but then the full cycle of Cl2/HOCl results in pH neutral outcome ... is this true even when the suns UV rays are the main reason for Cl2 consumption? Or does the pH neutral result only happen when HOCl is oxidizing something in the water?

I suppose I can try switching the SWCG off tonight, and seeing if the 0.10 rise still occurs with it off ....

 

[mknauss]

SWCG has very little to do with pH rise in the bulk pool volume.

pH rises when there is excess carbonate alkalinity. It will stop rising when the pH reaches equilibrium with the existing carbonate alkalinity.

 

[Stoopalini]

SWCG has very little to do with pH rise in the bulk pool volume.

pH rises when there is excess carbonate alkalinity. It will stop rising when the pH reaches equilibrium with the existing carbonate alkalinity.

What do you mean by "existing carbonate alkalinity"? Do you mean when the amount of carbonate alkalinity in the water reaches equilibrium with the amount in the air above the water?

And if so, then aeration only speeds the process up, making the equilibrium happen faster ... but pH rise will stop once it is reached ... even if aeration continues afterward?

 

[mknauss]

The bulk of your TA is from carbonate. If you lower the carbonate alkalinity in the water, the pH rise will lessen. But your pH can then become unstable as you are right at the equilibrium point.

I am straying outside my line of expertise. Have you watched

 

[PoolGate]

Mine goes up that much as well. I am still adding close to a gallon of 20 baume per week. It is what it is.

 

[Stoopalini]

The bulk of your TA is from carbonate. If you lower the carbonate alkalinity in the water, the pH rise will lessen. But your pH can then become unstable as you are right at the equilibrium point.

I am straying outside my line of expertise. Have you watched

Yes, I have watched it and referred to it in my initial post when I stated:

Based on the YouTube stream TFP did on pH, I assume this wouldn’t be enough to account for the pH rising so quickly.

Everything I've read, and watched (both YouTube and Pool School) from TFP has suggested the pH should settle, and the SWCG won't cause the pH to rise any faster than it would without the SWCG (assuming no acidic products like Trichlor are being used instead). This is why I'm wondering if there's something else going on (like the suction side leak) in my pool which is causing it to rise this fast with a low'ish TA.

I think there's two points of discussion here, and I may be mixing them up ... one is the rate at which the pH is rising (which I think is what you're getting at with the carbonate alkalinity) and the other is the point where the pH will stop rising and settle. I think the latter is impacted by the amount of CO2 in the air, is it not?

So even if I slowed the rate down, by lowering the carbonate alkalinity of the water ... wouldn't the eventual resting place remain unchanged? And if so, this is what you meant by your comment about using the same amount of acid, just with more time between doses.

I still may try turning off the SWCG tonight, just as an experiment, to see if it makes any difference in the rate during the 12 hours overnight.

 

[mknauss]

And if so, this is what you meant by your comment about using the same amount of acid, just with more time between doses.

Borates will slow that down. You might go to 10-14 days between adding acid. Overall the same amount of acid will be needed.

That referenced using Borates.

 

[Stoopalini]

That referenced using Borates.

Understood ... but I thought the benefit of using Borates is that they act as a buffer, so you can bring your TA much lower than you could without them, which would bring the carbonate alkalinity way down without the risk of unstable pH

Then with Borstes in the water, it would now require more acid to affect the pH (like having a higher TA would), since there's a strong buffer in there resisting the pH movement.

So you slow the rate down, and instead of taking 3-4 days to reach equilibrium, it takes 10 - 14 days now. Once equilibrium is met (~8.1 in my case), you then add acid to lower it down to say 7.6

Without Borates, and a TA of say 60 ... it takes a mimimum amount of acid to bring pH from 8.1 to 7.6
With Borates, and the same TA of 60, it takes more acid due to the buffering capability of the Borates.

... or am I misunderstanding how this works?

 

[mknauss]

so you can bring your TA much lower than you could without them, which brings the carbonate alkalinity way down without the risk of unstable pH

That is not how I understand them.
It will take more acid to move the pH/TA with borates in the water.

 

[Stoopalini]

It will take more acid to move the pH/TA with borates in the water.

Right, I'm agreeing with you here. Related to point 1 (the rate of pH change), the Borates act as a buffer, and slow the pH change ... which also means you need more acid to lower it manually.

But related to point 2 ... the equilibrium state where the pH stops rising ... you made a comment that the pH is rising due to excess carbonate alkalinity in the water. And as it leaves the water, moving toward equilibrium, the pH rises. Once it reaches equilibrium, then the pH stops rising.

So if the carbonate alkalinity was brought way down, and the pH remained stable due to Borates acting as a buffer ..... would this not allow you to change the equilibrium point, and in turn lower the resting pH?

This is why I originally posted this in the deep end, knowing I'd be asking some in-depth questions about how all this works ... thanks for sticking with me as I learn