Adding acid without lowering TA?

[presence52]

I've been adding about 1 pint of the 31.45% hydrochloric acid to a 10k gallon pool every 1-2 weeks to maintain the pH around 7.6 (I used to target lower values, but I don't anymore). I wait until the pH drifts up to 7.8 or 8 before treating.

The TA continues to drop with each treatment, now it's 60. Should I add baking soda? I feel like this might be counterproductive since I'm using baking soda to fix a problem brought on by the addition of acid, and baking soda will raise the pH (admittedly, only by a hair).

Is there anything else I can do?
1) Is adding a little bit of acid at a time better than all at once, to minimize the production and outgassing of CO2 when the acid reacts with bicarbonate?
2) Should I consciously try not to cause aeration (avoid swimming/turn off pump, etc) after adding acid? If so, for what time period?
3) Should I just tolerate a lower TA in the hopes that I will eventually reach some equilibrium? I have noticed that I'm not adding as much acid now at a TA of 60 compared to 120 prior.

Also, at the risk of sounding like a total cheapskate... I have open boxes of baking soda in my refrigerator to deodorize it. Can I just take that "used" baking soda and use it to treat my pool?

 

[JamesW]

Try keeping the pH at 7.8.

 

[Shieldsfx]

Try keeping the pH at 7.8.

Use Borax First to set TA. After correct TA, use granular acid (not liquid) to gradually set PH. When adding acid, add evenly to deep end of pool. I assume you have. Salt pool, which gradually pushes PH up overtime?

 

[duraleigh]

Lower pH - use muriatic....TA also comes down

Raise pH - use borax.....it has little effect on TA.

Lower TA - acid and aeration method....see Pool School

Raise TA - use baking soda....it has little affect on pH

The suggested method for adding acid is in front of a return.

"Used" baking soda is just fine. Test TA after adding the calculated dosage.

 

[tstex]

Lower pH - use muriatic....TA also comes down

Raise pH - use borax.....it has little effect on TA.

Lower TA - acid and aeration method....see Pool School

Raise TA - use baking soda....it has little affect on pH

The suggested method for adding acid is in front of a return.

"Used" baking soda is just fine. Test TA after adding the calculated dosage.

Thank you Dave...you presented that in an excellent format. But, I have two questions:

Doesn't aeration raise the pH too, but how chemically does aeration [if it's raising the pH] lower the TA?

Finally, once you use Borax [if you never have], what else does it impact either positively or negatively?

Thanks again, tstex

 

[mknauss]

Aeration raises the pH due to CO2 outgassing. The acid lowers the TA when added to the pool.

Borax will primarily raise pH but will effect TA slightly. Sort of like baking soda raising TA and effecting pH slightly.

Also want to be sure it is understood that you should NOT use Dry Acid or sodium bisulfate. If at all possible, always use muriatic acid. The sodium bisulfate adds sulfates to the water which will corrode metal, plaster, etc.

Take care.

 

[duraleigh]

Thank you Dave...you presented that in an excellent format. But, I have two questions:

Doesn't aeration raise the pH too, but how chemically does aeration [if it's raising the pH] lower the TA?

Finally, one you use Borax [if you never have], what else does it impact either positively or negatively?

Thanks again, tstex

Well, the primary reason I would like folks to think of it in the way I presented it is so you can move ONE parameter at a time. It is often confusing to move two parameters at once and thinking of it as I posted minimizes ANY side effects and concentrates on what you are trying to do....doesn't eliminate side effects but minimizes them to the point where you don't have to consider them.

 

[needsajet]

Doesn't aeration raise the pH too, but how chemically does aeration [if it's raising the pH] lower the TA?

Only the muriatic acid will reduce the TA. Aeration can be used after to raise the pH quickly so you can safely add acid again, which reduces the TA below the number you achieved the first time you added acid.

The aeration is not lowering the TA, but rather making it possible for you to stay in a safe pH range and reduce TA again. So it's more of a technique or method. Hope that makes sense.

 

[duraleigh]

Only the muriatic acid will reduce the TA. Aeration can be used after to raise the pH quickly so you can safely add acid again, which reduces the TA below the number you achieved the first time you added acid.

The aeration is not lowering the TA, but rather making it possible for you to stay in a safe pH range and reduce TA again. So it's more of a technique or method. Hope that makes sense.

That is correct but I have always thought of that as just a little bit confusing. Ben Powell said it this way (paraphrase) "the ONLY way to lower TA permanently is through the acid/aeration process"

So, counting on acid alone to lower your TA will not work.....assuming you want your pH to stay where it is

 

[tstex]

Dave, Need and Marty,

thanks again guys for the clarifications and interactions.

I too try to only focus on one parameter at a time because setting controls elsewhere provides the mgmt of the issue at hand. The only time I try to engage in two at a time, is when raising CYA after TONS of rain and draining pool due to massive rainfall. This is the only exception I use pucks bc it gives me a bit of a break from having to add bleach, yet I'm accomplishing the goal of adding the CYA stabilizer, sanitizing and when I achieve my 40-50 CYA range, I then don't have to add as much bleach bc of sun depletion. W all the rains of Harvey [3 ft] , and many nice rains prior, my CYA was shot and so was my CH [250 to 150]. But I'm bringing that back up slowing too [10-15ppm per ap]

Thanks again,
tstex

 

[mas985]

Ben Powell said it this way (paraphrase) "the ONLY way to lower TA permanently is through the acid/aeration process"

With all due respects to Ben, that quote is not exactly correct but he may not have intended the way you are reading it either.

Adding acid always lowers TA permanently. The acid reaction is not reversible without adding something (e.g. bicarbonate) to the water. The only reason for aeration is because the process of lowering TA also lowers PH and to prevent PH from getting too low, you need the aeration if you want to continue lowering TA. The aeration lowers CO2 in the lower which raises PH. If you add CO2 to the water, it will lower PH but will not change TA which also proves that TA does not change with levels of CO2.

If you still don't believe this, it is very easy to test. After lowering TA with acid and measuring TA, put some of the pool water in a jar that can be sealed to prevent anything from being added to the water. Open it in several weeks and the TA will be the same as will PH.

This reference says basically the same thing:

Alkalinity - Wikipedia

 

[duraleigh]

We may need to create a new thread in the deep end. However, before we do, let me say that the TA/pH relationship has been the most difficult subject to nail down in the years that poolforum and TFP have been in existence......almost 15 I think.

I don't know if anyone can find Ben Powell's article on lowering TA but it is the explanation that has always made the most sense to me. This article Using Air and Acid to Quickly Get Perfect pH/Alkalinity - AQUA Magazine seems to support Ben's ideas. He doesn't say adding acid won't lower TA.....he says it will also lower the pH, too, and hence, you need aeration to bring the pH back up to where it was before without raising the TA.

Let's say your pool is:

pH - 7.4
TA - 140

You want to move the TA down to 80 but you want to leave your pH alone.

Acid brings the TA and pH down both at once so, without aerating (to return the pH back to 7.4) the process of adding acid alone does not work.

Another way of saying it might be that acid certainly lowers TA but that comes with a price........that price being an unacceptable pH

 

[mas985]

Acid brings the TA and pH down both at once so, without aerating (to return the pH back to 7.4) the process of adding acid alone does not work.

Another way of saying it might be that acid certainly lowers TA but that comes with a price........that price being an unacceptable pH

I agree with both comments. But TA should remain at the lowered value indefinitely until something is added to the pool to increase it again.

 

[needsajet]

The other thing that helps reconcile the information from Ben Powell is that any uncovered pool is also aerated, even when the water is dead still. It has a certain amount of surface area allowing a certain amount of carbon dioxide to leave the pool water and enter the atmosphere, causing pH to rise. (speaking only of pools with rising pH, of course!).

Providing extra aeration merely increases the surface area of water, allowing CO2 out-gassing to speed up (be it a fountain, air bubbler, or 10 kids having a great time!). This conveniently speeds up the pH rise, so you can safely lower TA again - sooner than you could if the water was left still. If you rely only on whatever normal aeration you have, and don't use extra aeration, the pH will still rise to the same point. It just takes longer to get there.

As mentioned in the article, you can also hasten TA reduction by taking the pH below safe swimming levels. Thankfully, one of TFPC's greatest qualities is that the methods keep the pool open, safe and ready for swimming! (not to mention gentle on plaster and equipment).