will increase in TA tend to keep pH from dropping?

[singingpond]

In contrast to most who post about pH changes, our experience is that our pool's pH consistently drifts down over time. It's been my impression, reading on the forum, that this is more common in the Northeast for some reason. During a typical summer I add a couple cups of borax, probably every two to three weeks. The usual signal is that family members complain of stinging eyes, and, sure enough, pH will be back down to 7.2 or so. I bring it back up to around 7.7, and the pattern continues.

TA consistently measures 70 or 80.

Adding the borax isn't a big chore... However, I'm wondering if raising TA somewhat will tend to keep the pH up where I want it. If so, any guesses on how high TA should be? If it's just a matter of going to 100 or 110 (ballpark) I'd be curious to make the experiment. If it's likely to take a lot more than that to see an effect, I probably wouldn't bother for this seasonal pool...

P.S. Chlorination is done with liquid chlorine, so the dropping pH is not from use of stabilized chlorine products.

 

[Donldson]

In your situation raising your TA to 100ish would probably help. Most likely you will find your pH more stable while your TA drops slowly, or so I have noticed in trichlor chlorinated pools. (I know you aren't using trichlor, just the best example I have)

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[singingpond]

Thanks! I'll try adding a couple of pounds of baking soda, and see if that changes the pH behavior of the pool over the rest of the summer.

I searched a bit for links explaining how this would work chemically (and I'll look some more), but not much luck so far, especially since the majority of pool owners seem to worry about rising pH.

 

[Donldson]

Chem Geek gives a brief explanation in this thread: How Does TA Affect pH?

Remember that TA not only buffers pH but is a SOURCE of rising pH itself. The reason is that TA is mostly a measure of bicarbonate and at a given pH this is also a measure of the amount of carbon dioxide in the water. Pools are intentionally over-carbonated. When this carbon dioxide outgases from the pool, it raises the pH with no change in TA. Lowering the TA level reduces this rate of outgassing as does targeting a higher pH level.

As for why your pH wants to drop, must be something acidic introduced in to your water. Have you tested your fill water or even rain water?

 

[singingpond]

So, conversely, increasing TA should increase the rate of carbon dioxide outgassing?

As for acidity increase, last year I read every thread I could find on the forum about pools with dropping pH, and no one seemed to have a definitive explanation. The people reporting the effect seemed to be mainly in this region of the country. I did measure rainwater pH a few times last year (collection was pretty ad hoc, just collecting from water puddles on top of the pool cover after rain) - it was acidic, but I'm not sure of exact values, since the reading was at the bottom of the pool pH color scale. I wasn't convinced that the quantity of rain water was sufficient to account for the pH changes in the pool. At the time I did some reading about acid rain, but I'm afraid I don't remember the details a year later.

I'll try measuring pH of rain water and fill water again. We don't do much refilling, so not sure the fill water pH would matter particularly. Our water is well water, and it does contain iron. I don't think the pool water has much remaining iron, however, as it precipitates and is filtered out during the first week after filling in early summer.

 

[pooldv]

Yes, increasing TA will increase carbon dioxide outgassing. You can add soda ash to raise PH and TA at the same time. Raise TA 10ish at a time and see how the PH reacts for a week or so.

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