TFP Expert Discussion - pH and Alkalinity

JoyfulNoise

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As an update to something that was quickly discussed at the end but not properly covered, there are ways to adjust pH without impacting TA even though I stated that the two are linked and there isn't a way to affect one without affecting the other. If one wanted to lower pH without the TA changing, the way to do that is through CO2 gas injection. CO2 injection creates carbonic acid (H2CO3) in the water which dissociates into an acid proton (H+) and bicarbonate (HCO3-). Since the carbon dioxide is adding both hydrogen and bicarbonate, the TA remains unchanged but the pH decreases.

If one wants to raise pH without substantially affecting TA, then one would use borax. Technically speaking borax raises both pH and TA BUT the contribution of borates to TA at normal pool pH levels is so small that one can consider it to be practically zero. Borax is also a moderately strong base so it raises pH substantially.

As you can see, the interplay between pH and TA can be subtle and complex.
 
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TexEdmond

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I'm in a situation where my CH (325) and TA (80) chemistry seems stable weekly but I'm still seeing pretty rapid pH rise (every 2-3 days adding acid, 2 gallons this week). I even got into a situation where there was some white dust on the floor of the pool one morning and pH got up as high as 8.2. Well water is around 200ppm TA and have only filled around 400gal in that time.

I have heard the suggestions loud and clear to "let it go find its level" but I also heard Matt saying he keeps his TA in the 60-80 range and only adds acid every other week.

Would it be worth me trying another big acid dump to try to get TA down in the 60s? Should I wait a week or so after adding in the last of my leftover trichlor and Cal-Hypo and just doing bleach before I install the SWG?
 
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markayash

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Mar 21, 2016
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Atlanta Ga
I'm in a situation where my CH (325) and TA (80) chemistry seems stable weekly but I'm still seeing pretty rapid pH rise (every 2-3 days adding acid, 2 gallons this week). I even got into a situation where there was some white dust on the floor of the pool one morning and pH got up as high as 8.2. Well water is around 200ppm TA and have only filled around 400gal in that time.

I have heard the suggestions loud and clear to "let it go find its level" but I also heard Matt saying he keeps his TA in the 60-80 range and only adds acid every other week.

Would it be worth me trying another big acid dump to try to get TA down in the 60s? Should I wait a week or so after adding in the last of my leftover trichlor and Cal-Hypo and just doing bleach before I install the SWG?
I also add acid every other week but 2 gallons last me 3 or 4 months. Following to hear what’s causing your ph swing
 

markayash

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Mar 21, 2016
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Atlanta Ga
Question regarding TA..My PH drifts up slowly form 7.2 to 7.6 and I add a little ( maybe 2 cups every 2 or 3 weeks ) and its fine..Just checked my TA and its 40..
Leave it as is or raise TA?
 

mknauss

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Leave it as is or raise TA?
5 months ago your CYA was 60. Is it still?

You should keep TA at or above 50 if you have normal levels of CYA. Let the pH rise to 8 prior to lowering it to 7.6. You may find your pH rises ceases.
 

Leebo

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Question regarding TA..My PH drifts up slowly form 7.2 to 7.6 and I add a little ( maybe 2 cups every 2 or 3 weeks ) and its fine..Just checked my TA and its 40..
Leave it as is or raise TA?
My mind says allow your pH to increase more. Don’t correct until you’re closer to 8
 

Lineman7

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Awesome discussion, gents! Thanks for sharing.

I learned a lot.
 

markayash

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Mar 21, 2016
3,524
Atlanta Ga
5 months ago your CYA was 60. Is it still?

You should keep TA at or above 50 if you have normal levels of CYA. Let the pH rise to 8 prior to lowering it to 7.6. You may find your pH rises ceases.
Haven't checked my CYA since opening and was shocked to see it low. Still clear at 30..Still added a little but will get it back up.
I keep it on the lower side since my pool is 100% shaded after 3pm.
 

mknauss

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Adding CYA will add some TA.
 
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TexEdmond

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Jun 16, 2021
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If you have issues with high TA and pH, the last thing you want to use is Cal Hypo. That pushes up pH when used.
Good to know. I'll dump in my last 2 bags and eliminate that as a variable. It's free chlorine and I don't know how to safely dispose of it otherwise.

After watching the pH / TA symposium that might make more sense. Adding calcium means more carbonate in the pool, which dissociates to carbonic acid, which offgasses as CO2 which raises the pH? Six degrees of Alkevinity Bacon!

I have a few pounds of granulated trichlor and some pucks to get my CYA up then it's 100% liquid for me until I get the SWG installed.

And speaking of... Looky what I just found on my front porch!!!
 

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TexEdmond

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Witches GIF by memecandy
 
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TexEdmond

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I'd bet it'd dissolve a whole gob of carbon dioxide in your pool, which'd probably temporarily drive your pH down at least a little? Sortof a temporary CO2 injection system? I'd wonder if there'd be any risk to thermal contraction / plaster damage wherever it landed on the floor of the pool?
 

markayash

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Mar 21, 2016
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Atlanta Ga
I'd bet it'd dissolve a whole gob of carbon dioxide in your pool, which'd probably temporarily drive your pH down at least a little? Sortof a temporary CO2 injection system? I'd wonder if there'd be any risk to thermal contraction / plaster damage wherever it landed on the floor of the pool?
It floats until it dissolves, it’s still bubbling 😇
 

TexEdmond

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It floats until it dissolves, it’s still bubbling
Oh that's cool. Every time we put really big chunks in the laundry sink they'd sink and freeze themselves to the stainless steel.
 

mknauss

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True -- we do not want people to use it for that purpose.
As the video describes, TA is made up various form of alkalinity. Primarily carbonate, cyanurate, and boric.
 

nikolausp

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Jul 16, 2020
136
Houston, TX
My mind says allow your pH to increase more. Don’t correct until you’re closer to 8

When I allow my PH to get to 8.0, then I lower it to 7.6, it's back to 8.0 in 48 hours.... it's been confusing. Before adding Salt to the pool, going from 7.6 to 8.0 was more like 5 to 7 days.

This happened again just this week. Sunday evening PH was 7.6, and Tuesday evening PH was 7.8. CYA is 70, TA is 70.

Just curious, does CH level have any effect on the speed of PH rise?
 

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