TA not dropping with acid addition

[jmhawkins]

Once I got my TFPro test kit, it got a TA of 120. I've been testing pH daily, and it's been slowly creeping up (expected, I have a SWG and a waterfall people like). It hit 8.0 last week, so I added 8 oz of 31% Muriatic Acid (poolmath says this should drop my ~3500gal pool pH by about 0.5 and TA by 8 or 9). pH dropped to 7.5, but TA remained 120. This week, pH got back up to 7.8, so I added another 8oz of Muriatic Acid, and pH dropped as predicted to 7.2.

TA is still 120.

I'm not terribly worried about it, but curious why I'm not seeing TA drop like I would expect.

 

[PoolStored]

SWG and a waterfall people like

SWG does not raise pH. Waterfall will.

Lowering TA is a process. Have you checked your fill water TA? How much fill have you added.

 

[mShark]

You will find the answers you need here: Lower Total Alkalinity. In my case I don't see the TA move until the pH has dropped below 7.2. I had success with dosing my pool down to a bit above 7.0, and starting aeration at the same time to start bringing the pH back up. A couple of times through that cycle and it dropped the TA 10 points. It isn't particularly fast but it works.

 

[jmhawkins]

SWG does not raise pH. Waterfall will.

Lowering TA is a process. Have you checked your fill water TA? How much fill have you added.

No fill water added (negligible rainfall) since before the acid additions.

Huh, I thought I read that SWG raised pH, thanks for the correction.

 

[jmhawkins]

You will find the answers you need here: Lower Total Alkalinity. In my case I don't see the TA move until the pH has dropped below 7.2. I had success with dosing my pool down to a bit above 7.0, and starting aeration at the same time to start bringing the pH back up. A couple of times through that cycle and it dropped the TA 10 points. It isn't particularly fast but it works.

Ah, thank you, I assumed adding the acid would lower TA regardless of how low the pH went. I'll target 7.0 with the next addition.

 

[Jimrahbe]

jm,

Lowering TA from say 120 to 50 or so will take a couple days.... It is not a one time thing..

1. You basically have to test pH and TA and record what you have. Then add acid to lower pH to 7.0 or so.. Turn on some aeration, like a waterfall..

2. Wait about two or three hours and do it all again.. Over and over and over every few hours. At first the TA change will be very small. But over time the amount of change seems to get bigger and bigger.

When I had to lower my TA, I would start in the morning and do it all day until it was time to go to bed.. I'd then start the next morning and do it all over again..

If I were shooting for a TA of 60, I would drop the TA until it read 50 and stop. The next day it will be back to 60.

Thanks,

Jim R.

 

[cwswifty]

SWG does not raise pH. Waterfall will.

Hey @PoolStored. I've heard some say a SWG does raise pH and others say it does not. Seems to be debated quite a bit. From my limited experience it surely seems to. Not trying to argue the point one way or the other but wanting to better understand. Do the thousands of tiny hydrogen bubbles that shoot out of the returns, float up to the surface and pop while the SWG is producing not help CO2 to outgas and raise pH?

 

[PoolStored]

The OH- created would increase pH … but, when chlorine gas dissolves in water, some amount of hypochlorous acid formation does offset that pH. And then, over time, the disinfection/oxidation reactions tend to be acidic so on net balance, the SWG is mostly pH neutral.

What causes permanent pH rise is the offgassing of CO2 from the pool water. SWG aeration contributes to tha,t but so does just air movement over the water. Pool water is highly saturated with CO2 relative to the atmosphere so outgassing is proportional to the carbonate alkalinity concentration.

The “pH rise” effect of an SWG is somewhat psychological in nature. Pool owners typically chlorinate with acidic solid chlorine products (trichlor pucks and Dichlor powder). So when they stop using that in favor of an SWG, a highly acidic chemical source is removed and the natural pH rise from CO2 outgassing becomes more apparent. They also have been maintaining a higher level of TA to offset the acidic nature of the pucks.

Low pH and high TA is what causes pH rise.

PH TA Relationship - Further Reading

www.troublefreepool.com

 

[PoolStored]

At a TA of 70, you pool is fairly stable at 7.8, no?

 

[cwswifty]

Thanks for the reply! My pool currently has a few things working against a slow pH rise. New pool, pebble was installed last October and I run my spas sheer spillover 24/7. I’ve run it 24/7 from the beginning. From last October to this spring (water temp in the 60s) I used nothing but liquid chlorine. My pH would hover in the high 7s for a couple weeks. Once the water warmed up and the SWG began production pH would get above 8.0 in 2 or 3 days. I lowered my TA down to 60 and that helped a bit. Maybe 4 or 5 days. Yesterday I’ve completed the process of lowering TA to 50. Hoping for a solid week without having to lower pH. Fingers crossed!!