Proper PH Level

[dmorriso]

I'm confused on what the right PH level is. The Pool School says that 7.7 - 7.8 is ideal, but consistently I see people in threads saying to maintain it at 7.2.

Is 7.2 just for SLAMing, and the higher PH for normal use? FWIW, I've been keeping mine between 7.5 and 7.8 with about a cup of acid a week (and raising TA to 100 when it hits 80).

Also, in general, why do we want PH slightly basic rather than neutral?

Thanks,
Dan

 

[Texas Splash]

Hi Dan. It's true that on the Pool School - Recommended Levels the range are listed as 7.5-7.8. The reason others have been lower at times varies based on each pool. Those with new plaster or lots of aeration find themselves continuously trying to stay a bit lower. You are correct that those who are starting a SLAM will try to be at the low end as well. In the end though, it's best to not go over 7.8, and try not go below 7.2. For some new pool members, it's just easier to say, "Stay in the mid-7s" since they are so overwhelmed with new pool info. As long as your pool and water are happy at one of the recommended pH range numbers, you should be fine. Hope that helps.

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Also, we adjust TA up or down to help keep the pH more stable. Those struggling with a high pH need a lower TA to help keep the pH low.

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Another item good to know about regarding pH is the CSI. When you have time, do this little experiment as a learning tool. Go to the Poolmath calculator and look at the CSI row (3rd from the bottom). Plug-in your current test numbers and see what the CSI says. Now the experiment ... watch that CSI number as you increase pH and/or TA a bit. Just try it. Watch how quickly that CSI number rises when you let pH go up, or let TA go up. When the CSI gets close to or over .6, you can get scale in your pool. Too low and it's a problem for plaster. It may not be an issue for you, but it's good to know about that item. So every once in a while, take a peek at that CSI number once all your tests are loaded. As long as you never let the pH or TA creep-up on you, your CSI will be fine. Just a good thing to know.

 

[chem geek]

I see people in threads saying to maintain it at 7.2.

Where do you see that? The only time we say to lower the pH to 7.2 or lower (7.0) is before a SLAM or when lowering TA with acid and aeration. It is sometimes lowered for certain treatments when required, such as when using some metal sequestrant products. However, for general maintenance when using a hypochlorite source of chlorine, having such a low pH target is often frustrating since pools are intentionally over-carbonated so will tend to rise in pH from carbon dioxide outgassing and that occurs more quickly when the pH is lower.

If you want to add less acid over time then don't raise the TA to 100 and instead let it drop lower to 70 (i.e. keep it in the 70-80 range) and just lower the pH to 7.6 instead. You may find it to be more stable. Not a big deal, either way. Your pool is somewhat higher in CH so you wouldn't want the pH to get very high, but 7.8 is no problem and has a CSI of just under +0.3 with a TA of 80 ppm. At pH 7.6 with TA 70 ppm, the CSI is near 0.

 

[dmorriso]

Thank you both; I'n pretty sure the 7.2 I was seeing was before a SLAM. Bottom line, now I understand how pH impacts things, and understanding is really (for me) the whole point of being on here - thanks.

 

[Gregory C]

The above posts are spot on.

Just to add - for my particular pool situation - the well water that I fill my pool with comes out of the ground at about 350 - 375 ppm T/A - quite high to say the least. Muriatic acid does nicely in bringing the T/A down to acceptable levels. It also tends to keep my pH fairly constant at about 7.2 - 7.4 - given normal circumstances. 7.2 - 7.4 works for my particular situation but may not be appropriate for other situations.