pH buffer other than TA?

sbcpool

Well-known member
Mar 10, 2015
497
Upland, CA
I have repeatedly measured my TA at 80 ppm with the TFT test kit. It has been more or less the same for more than 5 years. However, I have to input 200 ppm in Pool Math to get the amount of HCl required to achieve the desired pH change. It takes about 64 oz. of 31.45% HCl to drop the pH from 8.2 to 7.5. It only takes two or three days for the pH to return to ~8. I have never added borates. I considered that maybe aeration was raising the pH, but shouldn't that lower TA?
 

cme4oil

Bronze Supporter
Sep 19, 2019
43
Phoenix Arizona
You can go lower on the TA, I have mine at 50 which is “finally” helping my PH issue. Mine sounds a little like yours, I even purchased Boric Acid to add to my pool once I know it’s stable. I have not committed 100% to adding any borates yet but I did already buy some in anticipation of doing it. The Boric Acid can help stabilize the PH as well but you really want to be pretty stable before going there.
 

Brett S

Well-known member
Mar 15, 2019
647
Orlando
I’m not totally sure what you’re asking here. 64oz of 31.45% muriatic acid should lower the pH in 20,000 gallons of water by about .8, so that seems to be about in line with what you are seeing. It should also lower the TA by about 13. So if you are frequently adding acid to your pool then TA should be trending down. However, if your fill water (or even your rain water) has a high TA, then that could be offsetting the acid and keeping your TA number from falling.

Aeration alone won’t lower TA (or really affect TA at all), however aeration will definitely raise pH, so if you have a lot of aeration that could definitely explain why your pH keeps rising. Now, with that said, aeration will indirectly lower TA because as the pH is raised you need to add more acid to lower the pH and the acid will also lower the TA.
 

sbcpool

Well-known member
Mar 10, 2015
497
Upland, CA
I’m not totally sure what you’re asking here. 64oz of 31.45% muriatic acid should lower the pH in 20,000 gallons of water by about .8, so that seems to be about in line with what you are seeing.
Pool Math app says 20,000 gallons at pH 8.2 with a TA of 80 needs 28 oz. 31.45% muriatic acid to reach pH 7.5.

EDIT - The "Effects of Adding" section shows 64 oz. as you describe, but when I select the pH tile on the overview it shows that for a TA of 80 and pH 8.2 I need to add 28 oz. Not sure what's going wrong here since there is only one pool set up, and it's set at 20,000 gallons.
 

sbcpool

Well-known member
Mar 10, 2015
497
Upland, CA
Dang it! 64 oz divided by 28 oz is 2.2857142857. I knew I recognized that number, but I couldn't place it. It's the ratio of grains (1,000) to ounces, precisely. Is there a back end problem converting units?
 

sbcpool

Well-known member
Mar 10, 2015
497
Upland, CA
Yeah, that's wrong. There is an error in the calculation when accessing it from the pH tile on the overview. It works correctly from the "Effects of Adding" feature. The error is precisely the same as the ratio of 1,000 grains to ounces. It could be coincidence, but it's a mighty coincidental one to match all the way out past ten decimal places.

The amount of 20° Baume HCl to go from 8.0 to 7.5 should be 23 x 2.2857142857 = 52.57 oz.
 

YippeeSkippy

Mod Squad
LifeTime Supporter
Jan 17, 2012
13,845
Evans, Georgia
Well I'm not vying to be the smartest guy by using PoolMath so I take it for what it says... who am I to argue? :laughblue:

I did the math via the old version of PoolMath found at bottom of the page.

Since its hardly a big deal why not just start half way or so.... retest...and re-dose as needed so you don't over shoot?? That sounds like the safest bet to me.
 

sbcpool

Well-known member
Mar 10, 2015
497
Upland, CA
Trial and error is relatively easy, but Pool Math is supposed to relieve us of that chore. There's something not right since part of the app calculates the same amount I see in practice, and the other part calculates an amount that's too low.
 

YippeeSkippy

Mod Squad
LifeTime Supporter
Jan 17, 2012
13,845
Evans, Georgia
@Leebo can you look into this please?

That the scale of the pH test tops out at 8.2....you may actually be higher. So doing things in smaller steps is a safer way since you can;t be positive you're at 8.2.
 

sbcpool

Well-known member
Mar 10, 2015
497
Upland, CA
The same error exists on the Web-based Pool Math. If you enter a 20,000 gallon pool with a TA of 80, pH 8.2 , and a target pH 7.5, it will advise you to add 28 oz. of 20° Baume HCl. However, if you scroll to the bottom of the page and enter 28 oz. of 31.45% HCl in the "Effects of adding chemicals," you will get: lower pH by 0.34.
 

samhorowitz

Bronze Supporter
Jan 28, 2020
28
FL
For me I get pretty similar results between “effects of adding” and the pH tile. Note that only the latter factors in your actual pool chemistry.