Aeration no longer increases pH

Problems relating to pH and total alkalinity.
Increase ph, increase TA. Reduce pH, reduce TA.
pH chemistry advice and techniques for the pool.
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Aeration no longer increases pH

Postby Eddles » Thu 29 Aug, 2019 19:13

Hi all, I took over responsibility of a swimming pool and hot tub back in April and due to not being trained properly, I wrecked the chemical levels of the pool and the hot tub. I'm slowly getting it all back in control. One issue I was having is was high TA but low pH. I was advised by a few helpful & patient people here to aerate the pool then lower the pH and TA, then aerate overnight and so on. It worked fantastic for a while and I got the TA down from 250 to 140, by bouncing between pH 7.0-7.4 using dry acid & aerating. However, aerating no longer affect the pH at all and it seems that the pH is going down, and down! I think it's about 6.7-6.8 at the moment. I'm a bit confused why the pH is dropping like a stone despite the aerating and using sodium hypochlorite which is a strong alkaline? What am I doing wrong here? Currently due to the insane cyanuric acid levels (about 200), I'm adding about 9 litres sodium hypochlorite every night as recommended by the Pool Calculator and getting an average FC level between 1-3, and TC level no more than 1ppm above the FC level. I will be draining the pool next month to fix the cyanuric acid problem for one and all, but I need the pH to be a lot more stable til then, after all, it was quite stable at 7.4 until a few days ago? What am I doing wrong?

Many thanks for your time!

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Re: Aeration no longer increases pH

Postby Teapot » Thu 29 Aug, 2019 19:40

Hi Eddles,
A couple of things spring to mind.
A cyanuric acid level of 200 you know is way to high but it also a forms a pH buffer in opposition to TA. It sounds as if this is pulling the pH down and aeration lowering the TA is now too low to fight it back up.
As the level of TA lowers it takes longer for the aeration to work.

Although sodium hypochlorite has an alkali remnant at a lower pH it forms hypochlorous acid and that can, in high concentrations at the amount you are adding, lower the pH.

You really do need to lower the cyanuric acid level to get back control.
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Re: Aeration no longer increases pH

Postby Denniswiseman » Fri 30 Aug, 2019 02:57


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