pH 7.2 to 7.8 in a day

[DrewLG]

I recently finished a SLAM and now I'm trying to lower TA. I measured pH at 7.8 using the phenol red comparator test, added muriatic acid, and after a couple hours measured pH at 7.2.

One day later, the pH is back at 7.8. I ran the spa for a couple hours during that time, but there was no other aeration. Is such a rapid pH rise expected?

 

[B_A_T]

I am having similar issues, I lower my PH to 7.2-7.4 and within a day it is in the high 7's and the next day it is >8. It is a new plaster pool (started up this spring), all my chemicals seem to be in line, I just can't seem to keep my ph down for more than a day.

 

[proavia]

I recently finished a SLAM and now I'm trying to lower TA. I measured pH at 7.8 using the phenol red comparator test, added muriatic acid, and after a couple hours measured pH at 7.2.

One day later, the pH is back at 7.8. I ran the spa for a couple hours during that time, but there was no other aeration. Is such a rapid pH rise expected?

With your last reported TA of 140 and a couple hours of running the spa, that isn't too surprising.
What is the pH, TA and CH of your fill water.

 

[proavia]

I am having similar issues, I lower my PH to 7.2-7.4 and within a day it is in the high 7's and the next day it is >8. It is a new plaster pool (started up this spring), all my chemicals seem to be in line, I just can't seem to keep my ph down for more than a day.

New plaster will cause the pH to rise quicker. Also, a TA of 90 may cause it to rise a bit faster.
With continued acid additions to keep your pH in range, it will slowly lower theTA. Once theTA gets down to around 60, you will find the pH rise will slow a bit. You might see a quicker pH rise for about a year or so with new plaster.

 

[DrewLG]

With your last reported TA of 140 and a couple hours of running the spa, that isn't too surprising.
What is the pH, TA and CH of your fill water.

Good to know that it's not abnormal. Thanks.

Fill water specs are in my signature -- pH 7.5, CH 150, TA 170 -- but I haven't added any water since starting to lower TA.

 

[wireform]

It's also the nature of the beast that when you knock it down in big drifts it'll bounce back more vigorously. Small bites work better and there's nothing wrong with a PH 7.6-7.8 except for new plaster being the exception.