pH & TA relationship

[alexsmith1]

Hi all,

After having a new pool for about a year now, I'm starting to figure out it's weekly routine on when to add acid. My question is, if my pH is 7.4 TA is usually around 80ppm. However when the pH rises to around 7.8-8 it jumps to 100-120ppm. Is this normal?
I find myself adding 2 cups of acid a week to drop it from 8-8.2 down to the mid 7 range.

Thanks!

 

[ajw22]

What is the pH and TA of your fill water?

Do you have an autofill on the pool or how often do you add water to replace evaporation?

 

[aussieta]

ta will not increase on its own
ta test are you wiping the reagent tip between drops as it is prone to static electricity
why are you trying to keep you ph so low, if you let it raise to 7.8 it will not increase as fast

 

[alexsmith1]

pH = 7.2
TA = 70

No autofill, however filling up probably once every 2 weeks due to evaporation. Thanks.

What is the pH and TA of your fill water?

Do you have an autofill on the pool or how often do you add water to replace evaporation?

 

[alexsmith1]

I never wipe down the reagent tip. I do add 1 drop and put the lid back on.

I never try and keep my pH that low, what I'm saying as a reference is if my pH is under 7.8 the TA is around 80, however when it gets to 8-8.2 the TA will jump to 110..
I try to keep my pH at 7.7-7.8 ideally and add smaller amounts of acid to bring it down. Thanks

ta will not increase on its own
ta test are you wiping the reagent tip between drops as it is prone to static electricity
why are you trying to keep you ph so low, if you let it raise to 7.8 it will not increase as fast

 

[ajw22]

What test kit are you using?

Post a complete set of test results.

Read the Notes in...

Total Alkalinity

A drop-based test used to measure the alkalinity in water. Alkalinity helps serve as a … Read more…

www.troublefreepool.com

Notes

• Sometimes a static electric charge can build up on the R-0009 dropper bottle tip, causing the drops to be smaller than usual and making the test read higher than actual. You can prevent this by wipping the tip of the dropper bottle with a damp cloth or tissue before you start and after each drop.
• Hold the dropper bottles vertically and squeeze gently, so that drops come out slowly and seem to hang on the tip of the dropper bottle for a moment before falling.

 

[alexsmith1]

@ajw22 thanks for the reply.

I use the clear choice labs test kit today's readings are:
pH: 7.8
TA: 90
CH: 400
CYA: 70
FC: 5ppm
CC: 0ppm
Water temp: 29c / 84f
Sorry I don't have a salt reader..

Now I'll re-test it in a few days time and the pH will rise to 8-8.2 with a TA of 100+ so bizarre..

 

[ajw22]

Please post all your test results and chemical additions and let us see what happens. PoolMath makes it easy to log test results and chemical additions and share the test logs.

 

[alexsmith1]

Hi @[B]ajw22[/B], I won't will probably add a few cups of acid in a couple of days pending pH reading. Thanks!

 

[ajw22]

What type and strength acid are you using?

 

[alexsmith1]

Hydrochloric Acid - unsure on the strength but it's Dang strong! Thanks.

 

[tumor]

TA does change with pH. I've seen a similar increase/decrease in my pool. I'm not a chemist so I can't explain the exact reasoning (its something to do with the equilibrium of the dissolved chemicals in the pool at that specific pH). Two references that confirm that TA changes with pH:

1.) Taylor has a Total Alkalinity to Carbonate Alkalinity conversion table in its booklet for CYA and Borates that is dependent on pH level
2.) TFP article on lowering TA states:

"Add acid to lower your PH to between 7.0 and 7.2 (this also lowers TA)"
"Aerate until PH rises to around 7.6 (the only way to raise PH without also raising TA)"