How important is Alkalinity?

dalu

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Aug 3, 2022
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I just installed my new pool a couple weeks ago. Initial fill was from a water truck and topped off with my local well water. Total Alkalinity was high from the start. I only had the pool store supplied test strips to test alkalinity which measured around 200 ppm. Over the course of several days, I added 3 gallons of Kleen Strip Green Muriatic Acid, which is all I could find locally. From what I've been able to determine, this might be 20%...or could be even lower. All the SDS says is "less than 30%". Got my hands on a few gallons of the 31.45% acid and added 43 oz about a week ago.
Through all this, the test strip reading was jumping around. 200, 180, 150, 120, 180, 100, etc., so either I am terrible at reading the colors or the strips aren't very accurate.

My Taylor K-2006 kit arrived a few days ago, and this read 200 first time I tested, and 160 after adding 56 oz. of the acid two days ago. Currently waiting for pH to raise enough to add more acid. Everything else is testing fine.

So...my question is: How worried should I be about the high Alkalinity? Should I just slowly lower it whenever my pH is high enough to add MA? Not worry about it at all?
 

Texas Splash

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or the strips aren't very accurate.
^^ That. Now that you have a K-2006 just use that. TA is notoriously high in your area. It will fall with repeated acid treatment. While you don't want an astronomically high TA, usually managing the pH is more important than TA. Let the pH hit 8.0 then use enough acid to lower the pH to about 7.0-7.2. That will put a small dent in the TA each time you do it. Once you get the TA down to 120 or below, if the pH is happy and not rising too fast, you don't have to work about the TA as much.
 

IceShadow

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You can speed up the pH rise with aeration by running all your features after lowering pH per Texas Splash, which will speed up the time between acid adds, working down your TA faster.
...though this usually isn't needed, as high TA only has two downsides:

- It will push your CSI higher and if your CH is also high, it can mean you are at risk of calcium deposits forming
- It will make your pH rise faster

The first one above is the only real reason to push down TA aggressively. So if your CSI is high and you need to lower your TA to get your CSI in check, aerate and acid away. The second downside is a self-correcting problem, as you'll add acid to make your pH go down, which will lower TA as you go.
 

Toxophilite

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...though this usually isn't needed, as high TA only has two downsides:

- It will push your CSI higher and if your CH is also high, it can mean you are at risk of calcium deposits forming
- It will make your pH rise faster

The first one above is the only real reason to push down TA aggressively. So if your CSI is high and you need to lower your TA to get your CSI in check, aerate and acid away. The second downside is a self-correcting problem, as you'll add acid to make your pH go down, which will lower TA as you go.
Of all parameters of my pool, the day I long for is when I'm not fighting the pH rise. Your info makes good common sense in the face of CSI management. My CSI is currently -.04 and has never been higher than .2 either direction. Pool Math will call for all TA measurements out of range as needing lowering pH and aeration, but I have long been able to keep my TA stable at 80 with small maintenance MA doses only. But, recently it crept high again. But, as you say, my testing showed TA higher than my norm, but CSI well within range near -0-.
 

dalu

Member
Aug 3, 2022
17
mi
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15000
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Chlorine
Liquid Chlorine
Oh, and welcome to TFP! :wave:

Visit our Pool Care Basics page for more info.
Thank you for the quick responses and warm welcome! I will continue my current path and hopefully will eventually get alkalinity down where it belongs.

I turned the return jet upward so it's rippling the surface, but that's about it for aerating the water.

CH is 170-180 and CSI was 0.4 before latest acid treatment and -0.45 after when both alkalinity dropped to 160 and pH dropped to 7.0. I didn't test CH this morning, but assuming it hasn't changed and with pH up to 7.4, CSI should be around 0 to -0.1, so I think I'm ok there.
 

Texas Splash

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CH is 170-180 and CSI was 0.4 before latest acid treatment and -0.45 after when both alkalinity dropped to 160 and pH dropped to 7.0. I didn't test CH this morning, but assuming it hasn't changed and with pH up to 7.4, CSI should be around 0 to -0.1, so I think I'm ok there.
With a vinyl pool and using liquid chlorine, CSI shouldn't be an issue for you to worry about. If you have a heater, then you may require a minimum amount of CH, but only if that's applicable.
 

IceShadow

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You don't want CSI too positive with vinyl, as it can precipitate out on the vinyl and cause scaling. But negative isn't too much of an issue with vinyl, so long as pH is in check.
 

dalu

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Aug 3, 2022
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mi
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15000
Surface
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Chlorine
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Continuing with the "wait for pH to rise, add MA" cycle which I understand. Tested this morning and TA is 110, so I'm slowly getting there, it seems. I'm not worried, but looking for feedback if the amount of change I'm seeing makes sense. Estimated pool volume is 15000 gallons.

8/4 I measured 7.6 pH and 150 TA. Added 64 oz. 31.45% MA.
8/5 I measured 7.2 pH and 120 TA. (PoolMath says this should have lowered pH 1.02 and TA by 17.)

8/7 I measured 7.6 pH and 120 TA. Added 70 oz. MA.
8/8 I measured 7.2 pH and 110 TA. (PoolMath says this should have lowered pH 1.12 and TA by 18.)

Individually these treatments had significantly different actual results (-30 TA vs. -10 TA) but taken together it's actually not far off from calculated (-40 TA actual vs. -35 TA calculated). Just wondering if this is normal.
 

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mknauss

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Just wondering if this is normal.
The resolution of the TA test is not perfect. So that can skew your results. Say the initial test the real TA was 142, and after adding acid it was 125. Those would be the 17 ppm expected drop, but your test resolution is such that it cannot see those data points.

Same with the next add. 125 would be 107. Same thing on the testing.

So do not try to get too precise. This is hand grenade throwing, not horseshoes.
 

PoolStored

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This is likely testing error. The tip of the acid bottle in the test gets a static charge and can alter the size of the drops. Use a wet towel and wipe the tip in between drops to eliminate the charge.