Chasing the perfect TA

danielduerr

Gold Supporter
Nov 2, 2016
10
Carmel Valley, California
Hello fellow TFP members!

I've been following the TFP methods of pool chemistry for 3+ years now and love everything about it, the quality of the water itself being paramount above all else. I've read the ABCs several times and understand both the target levels as well as the qualitative rules (e.g. don't chase a number for the sake of chasing a number). As such, I felt inclined to post this message and get some feedback.

Here are my latest test results:
FC 8.0
pH 7.4
TA 90
CH 450
CYA 15
Salt 3400
Temp 88
CSI -0.06

My CYA is normally 75 but I've been guilty of not testing it enough this summer, working on dosing it back up now. My FC is a little high due to a couple weeks of minimized pool use. But overall I believe my pool is well balanced. And the water feels/looks amazing.

All that said, I'm wondering if I am guilty of chasing a number when it comes to TA. I've become quite good at the acid + aeration process, having performed it 5 times this pool season, and it yields the expected result. But eventually my TA finds its way back to where it is now and seems to be comfortable/stable there. Having done all this more than a dozen times, I'm starting to think I am fighting something that may not need to be fought. And, my pool is covered and not leaking (confirmed by monitoring auto-fill usage) so I don't think this is the case of fill water driving TA back up.

What do you all think? Am I chasing a number here, or am I just not pushing the TA down low enough during aeration? Looking forward to some feedback.

Best,
Daniel
 

Msch99

Gold Supporter
Bronze Supporter
Jun 11, 2018
380
Verona, MO
I am lucky, last added MA on 7.27. TA at 80 and PH just now reaching close to 7.8, slow climb for the last 30month. Pool covered with solar cover except when swimming or robot in.
 

Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
14,186
Bedford, TX
Daniel,

Most SWCG pools like their pH at about 7.8... Why are you forcing it down to 7.4..??? I would not adjust TA unless it drops below 50 or becomes so high that you can no longer stabilize pH.

As you already know, you need to get your CYA back up to 70 or so...

Thanks,

Jim R.
 
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mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,707
Pleasanton, CA
All that said, I'm wondering if I am guilty of chasing a number when it comes to TA. I've become quite good at the acid + aeration process, having performed it 5 times this pool season, and it yields the expected result. But eventually my TA finds its way back to where it is now and seems to be comfortable/stable there.
If your TA is rising constantly, more than likely your fill water has high TA in it. That is my issue and I stopped trying to lower TA. It really isn't worth the effort and there are other ways to handle high TA/PH.

Because I have a plaster pool and SWG (as do you), I try to keep CSI slightly negative by limiting PH and then TA takes care of itself. However, this does mean that I need to add acid fairly often because my fill water has very high TA, CH and PH. Plus we don't get much rain in the summer and evaporation is quite high so I added an auto acid dosing system. The only thing I target now is FC, CYA and PH/CSI. TA and CH I monitor to calculate CSI but I do not directly try to change those since the fill water is constantly adding those anyway. The constant addition of acid keeps TA in a respectable range (70-90 ppm) and compensates for the high CH levels.
 
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danielduerr

Gold Supporter
Nov 2, 2016
10
Carmel Valley, California
Daniel,

Most SWCG pools like their pH at about 7.8... Why are you forcing it down to 7.4..??? I would not adjust TA unless it drops below 50 or becomes so high that you can no longer stabilize pH.

As you already know, you need to get your CYA back up to 70 or so...

Thanks,

Jim R.
Thanks @Jimrahbe ! I'll take that as a +1 on "stop chasing the number". :)

I do my main pool maintenance on the weekend, thus a weekly regime, so I target 7.4 as acceptable pH knowing it'll be around 7.8 by the next weekend. I'm also largely trying to manage things to a slightly negative CSI which I think I've got in balance on this.
 
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danielduerr

Gold Supporter
Nov 2, 2016
10
Carmel Valley, California
If your TA is rising constantly, more than likely your fill water has high TA in it. That is my issue and I stopped trying to lower TA. It really isn't worth the effort and there are other ways to handle high TA/PH.

Because I have a plaster pool and SWG (as do you), I try to keep CSI slightly negative by limiting PH and then TA takes care of itself. However, this does mean that I need to add acid fairly often because my fill water has very high TA, CH and PH. Plus we don't get much rain in the summer and evaporation is quite high so I added an auto acid dosing system. The only thing I target now is FC, CYA and PH/CSI. TA and CH I monitor to calculate CSI but I do not directly try to change those since the fill water is constantly adding those anyway. The constant addition of acid keeps TA in a respectable range (70-90 ppm) and compensates for the high CH levels.
Thanks @mas985 . You've actually been a source of comfort in my past learning of the ABCs because I noticed you had a similar setup and also were in CA where we have traditionally high TA/CH in our fill water... I've been admittedly dosing more acid these past few weeks trying to see if the constant 7.0-7.4 + weekly aeration would help me get my TA number down where I want it. If I call it a day on the current numbers I have and just accept a 90-100 TA as acceptable, I can get by with minimal acid dosing each week with everything remaining nicely balanced. Like you, I largely focus on my CSI as an indicator of overall balance in the water.

Did you design your own acid dosing system? Just curious.
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,707
Pleasanton, CA
Did you design your own acid dosing system? Just curious.
Yes, see link:

 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
15,796
Tucson, AZ
The concentration of CYA is not affected by adding acid to lower TA. All cyanurate species that contribute to the cyanurate portion of TA are dissolved "solids" at standard temperatures and pressure unlike carbonate alkalinity which contains an aqueous gaseous species at standard temperatures and pressure (ie, dissolved CO2).
 

JamesW

TFP Expert
Mar 2, 2011
16,336
Adding cyanuric acid doesn't change the TA.

The cyanuric acid is C3H3N3O3.

As it dissolves into the water, some of the hydrogen ions separate from the main molecule.

The hydrogen ions lower the TA and the remaining molecule increases the TA by the same amount. So, the net effect is no change to the TA.

When you add acid, it's a bunch of hydrogen ions. This lowers the TA and the pH.

Some of the hydrogen ions connect to the cyanuric acid molecule.

So, the cyanuric acid molecule only differs in the number of hydrogen ions that are attached.

Cyanuric acid molecules with 3 hydrogen ions are called cyanuric acid. Cyanuric acid doesn't contribute to the TA.

Cyanuric acid molecules with less than 3 hydrogen ions are called cyanurate. Cyanurate does contribute to the TA.

The number of hydrogen ions that are attached is determined by the pH.

For example, at a pH of 6.88, about half of the cyanuric acid molecules have 3 hydrogen ions attached.

The hydrogen ion attachment sites are where chlorine atoms attach to cyanuric acid. They take open spots or they push out the hydrogen ions and take their spot.
 
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danielduerr

Gold Supporter
Nov 2, 2016
10
Carmel Valley, California
Thanks for the thorough explanation @JamesW! Very interesting. So are you suggesting that at a pH of 6.88, the other half of the cyanuric acid molecules have <3 hydrogen ions (e.g. cyanurate) and thus do contribute to the TA? Or are you saying that the net effect is no change?

Does anyone here know if Pool Math (app) compensates for this effect? I'm trying to decide if I should adjust my TA reading at all based on CYA level...
 

JamesW

TFP Expert
Mar 2, 2011
16,336
Cyanurate does contribute to the TA.

Poolmath does account for the effect.

When cyanuric acid is added to the water, the hydrogen ions that are released lower the TA as much as the resulting cyanurate raises the TA. So, adding cyanuric acid has no net effect on TA.

The rule that I use is that if the pH is constantly going too high, the TA is too high.

If the pH is constantly going too low, the TA is too low.

If the pH is stable, the TA is good.
 
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beautifulpool

Well-known member
Jun 2, 2019
101
North TX
Adding cyanuric acid doesn't change the TA.

The cyanuric acid is C3H3N3O3.

As it dissolves into the water, some of the hydrogen ions separate from the main molecule.

The hydrogen ions lower the TA and the remaining molecule increases the TA by the same amount. So, the net effect is no change to the TA.

When you add acid, it's a bunch of hydrogen ions. This lowers the TA and the pH.

Some of the hydrogen ions connect to the cyanuric acid molecule.

So, the cyanuric acid molecule only differs in the number of hydrogen ions that are attached.

Cyanuric acid molecules with 3 hydrogen ions are called cyanuric acid. Cyanuric acid doesn't contribute to the TA.

Cyanuric acid molecules with less than 3 hydrogen ions are called cyanurate. Cyanurate does contribute to the TA.

The number of hydrogen ions that are attached is determined by the pH.

For example, at a pH of 6.88, about half of the cyanuric acid molecules have 3 hydrogen ions attached.

The hydrogen ion attachment sites are where chlorine atoms attach to cyanuric acid. They take open spots or they push out the hydrogen ions and take their spot.
Mr James, can I ask you something?
If we have a 1 molecule of H2O and our water molecule Gains a Hydrogen Ion, & we get H3O+
If we have 1 molecule of H2O and our water molecule Looses a Hydrogen Ion &
we get H+ + OH-.... is this premise ok so far?
Question would the water gaining the ion
And the water loosing the ion, land on the two ends of the pH scale? (Real world more molecules more falling in between)
Hydronium
Hydroxide
 

danielduerr

Gold Supporter
Nov 2, 2016
10
Carmel Valley, California
@JamesW thanks again for the insight, makes a lot of sense. Great to know Pool Math accounts for the effect. I will treat the TA target as real and not try to compensate manually based on CYA. I ❤ Pool Math!

Update: After I started this post a few weeks back (at pH 7.4 / TA 90), I did the following:
  1. Brought my CYA back up to 75.
  2. Stopped worrying about my TA target and focused on pH/CSI only to see what would happen.
On Sep 7, I was at pH 7.6 / TA 110. On Sep 12, I was at pH 7.6 / TA 120. At this point, I decided I was going to worry about my TA target again. 😅

I suspect my approach to aerating has been flawed. On past attempts, I'd target the TA I wanted (70) and I'd stop adding acid/lowering the TA as soon as I hit that target, regardless of pH. But when I hit the target, my pH was usually around 7.1 or 7.2 because I'd just finished the process. So then when my pH rose to say 7.6, my TA would rise with it back up to say 90. From here, I'd manage my CSI by keeping my pH on the low end of the scale (7.2-7.4), and I'd just add a lot of acid every week.

This time around, I'm thinking I need to keep going until my TA target (70) is reached at the target pH (7.6). Am I thinking about this correctly?
 
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Msch99

Gold Supporter
Bronze Supporter
Jun 11, 2018
380
Verona, MO
Not an expert but from what I have read here there isn’t an exact perfect number for TA. Only a range. Each pool may have a slightly different sweet spot for TA and PH.
Your "Target TA" is where your PH rises the slowest. Mine is around 70 to 80. I last added MA on July 27th and my last PH check was around 7.6 to 7.7.

Some pools like a PH higher than 7.6 I have read. I would say to keep that in mind. If it hangs around 7.8 or so and doesn't go above 8 and your TA is within or close to your range, let it ride and be happy! So instead of lowering to 7.2 or 7.3 when it gets high, only add MA to drop a couple tenths to see what happens.
 

danielduerr

Gold Supporter
Nov 2, 2016
10
Carmel Valley, California
Thanks @Msch99! Makes sense. I'd rather achieve my target CSI with a higher pH / lower TA as it'll fluctuate less, require less MA, and be more in line with what my SWG prefers. Based on your feedback and a couple others up here, it's clear I was not going low enough since even at the TA 80 where I stopped, I saw a strong pH rise over the next week.
 

ckendalls

Active member
May 17, 2018
27
Clermont FL
Going through the same thing here with my 1 yr old pool. Gradually bringing down the TA to 50-60 and seeing of I can keep the pH 8.0 pr below without adding MA as often and without going too aggressively low on the CSI . So far, as I have dropped the TA the pH rise is definitely slowing and seemingly topping out lower when I extrapolate with the acid demand.

I also don’t think my CYA has to be at TFP recommended levels >60 for an SWG system either even here in sunny Florida. I’m sorry I went up to a CYA of 70 even in the dead of summer... Like many Florida pools, ours is in a screened enclosure so the sun effect isn’t quite as maximal and I have the SWG at less than 10% or just above zero for 8 hrs to keep the FC from going too unpleasantly high in this 11K gallon pool. A lower CYA will also raise the CSI a bit with the lower TA. I also now have a borate level at 50 ppm which some claim moderates the speed of the pH rise. I don't think I saw much difference...? Mainly I definitely like the water quality look and feel with the borate in there. With less rain now, the fill water may bring up the TA over time which I may have to fight and I may let the temp drop below the 80s so we’ll see how it goes. But thanks to TFP info, the pool has always sparkled and no equipment issues. Meanwhile my snowbird neighbor with his paid service has already had to change their salt cell twice on their year old pool, probably because they crank the SWG and don't manage the overall chemistry (based on my spot checks). But their water looks OK as nothing will grow when its pretty much SLAMed non stop...