Total Alkalinity and pH in a salt pool

[pwarbeck]

I recently filled a pool and have been trying all week to balance the chemistry. I make my own daily tests with a Taylor FAS-DPD kit and I confirm my test results by taking water samples to Leslie's. I have managed to get all the chemistry within recommended range except for pH and Total Alkalinity.

If TA is too high, I add the amount of acid recommended by Leslie's computer printout. This brings the TA within range but lowers the pH too much. So the next day's computer printout tells me to add soda ash. The soda ash brings the pH within range but also raises the TA too much. The next day's computer printout tells me to add acid. In fact, it tells me to add the same amount of acid I had added two days before. Clearly this is not working.

Currently pH = 7.4 and TA = 130. If I add a small amount of acid, I may be able to get the pH down to 7.2 or 7.3 and TA to 120, which is right at the upper limit. But given the fact that these two move in lock step, it seems that there is no way I'll be able to adjust both pH and TA to their ideal values (say 7.5 and 100). Or is there?

Is this a known problem? What's the solution?

 

[Oly]

Welcome.
The root of your issue is relying on pool store testing, a common problem that affects many frustrated pool owners who visit here seeking help.
If you have a good test kit Test Kits Compared use it to lower your pH into the low 7's then over time the pH will climb back and the TA will drop slowly. Monitor it yourself at home.
When your pH climbs above 7.9-8, only use muratic acid to lower pH and use PoolMath to calculate amounts and expected results. Test your water an hour after applying chemicals (pump running) to confirm results and monitor your pH after several days to check its rise. Eventually the TA will drop below 100 and the pH rise should slow.
I would also recommend testing your fill water for TA and CH, calcium hardness. If you have high levels of TA or CH in your fill water then it will raise your levels every time you add water for evaporation so be aware.

 

[Texas Splash]

The founding concept of TFP .... always test your own water with a reliable test kit. Trust your own testing. TFP and pool store generic recommendations are not designed to be compatible.

 

[IceShadow]

The pool store isn't going to tell you to aerate to raise pH. They're going to sell you a chemical to do it. That it raises the TA and then you get a recommendation to add acid (countering the chemical you just added to raise the pH) is a nice little bonus for them.

 

[pwarbeck]

Welcome.
The root of your issue is relying on pool store testing, a common problem that affects many frustrated pool owners who visit here seeking help.
If you have a good test kit Test Kits Compared use it to lower your pH into the low 7's then over time the pH will climb back and the TA will drop slowly. Monitor it yourself at home.
When your pH climbs above 7.9-8, only use muratic acid to lower pH and use PoolMath to calculate amounts and expected results. Test your water an hour after applying chemicals (pump running) to confirm results and monitor your pH after several days to check its rise. Eventually the TA will drop below 100 and the pH rise should slow.
I would also recommend testing your fill water for TA and CH, calcium hardness. If you have high levels of TA or CH in your fill water then it will raise your levels every time you add water for evaporation so be aware.

Excellent advice! I plan to follow it. No more trips to the pool store.