pH stubbornly high

[Mimi Pool]

Knock on wood, the only problem this season. The water has been crystal clear all year. Here are readings from yesterday (we use PoolMath to track all activity):
FC 6.5 pH 8.0 TA 85 CH 325 CYA 60 CSI 0.38 Temp 84
Acid was put in 6 days ago, dropped pH to 7.6 but it bounced back up; this has happened repeatedly. The only other comment I could make is we're getting what I think is mildew on the floating thermometer where it gets wet then dries, and in the skimmer above the waterline. Both clean off rather easily with Mr. Clean Magic Eraser.

Suggestions are appreciated.

 

[Texas Splash]

Next time your pH hits 8.0, trying using enough acid to lower the pH to about 7.2. That should help lower the TA each time and once the TA gets down to about 60, maybe even 50, your pH might stabilize a little better.

 

[mknauss]

pH rise is natural with carbonate alkalinity. You show a TA of 85. That result is not possible with your test kit. Do not interpolate. Once the sample does not change color using the R0009, that is your TA.

Have you been using fill water?

 

[Mimi Pool]

I just found out some of the readings are days old, will retest then post. We have not used any fill water. Great tip about lowering to 7.2, only thought had been to get it back to ideal range.

 

[Mimi Pool]

Just did the testing - good bit of rain yesterday and about to put in a gallon of chlorine.
FC 5 pH 8 TA 90 CH 325 CYA 60 CSI 0.39 Temp 82
TA and CH have been steady all year.

Just to explain the interpolation - using the smaller sample option, after 8 drops the sample turns from green to clear, after 9 it turns red. So 90 it is.

Unless anyone else has input, the plan of action will be to follow Texas Splash recommendation to lower pH to 7.2.

 

[HeyEng]

I have stopped fighting my PH. It wants to wander up to 8.0+ and no matter how many times I push the TA back down (hangs around 80-90) via the aforementioned TFP method, it invariably creeps back up. I think for some of us, it's just the way it is. My fill water (well) has a TA of 20, so I don't believe that is responsible.

Nonetheless, I don't use a whole lot of acid...about 4 cups a week to keep my CSI around 0 and pool clarity is great so I don't really sweat it too much.

 

[jark87]

I’ve also been fighting a more frequent than normal pH rise this year. From what I can discern, it’s mostly due to our continued drought, causing more evaporation, resulting in more frequent pool fills. Our fill line is above the water line, so filling causes aeration. In addition, our fill water has high pH and high TA. In the past, I’ve been able to keep TA in the 50-60 range which helped decrease the pace of pH rise. I just can’t get TA down to that level this summer, regardless of how much acid I add.

 

[Mimi Pool]

Update - turns out we were unable to get the pH all the way down to 7.2 though we didn't push it. Starting on 8/3 through 8/7 we put 12 lbs of dry acid in. After 10 lbs the reading was 7.4 so last night we put in another 2 lbs but it did not drop. Here are todays results:
FC 7.5 pH 7.4 TA 80 CH 350 CYA 60 Temp 83 CSI -0.20
So along with pH down from 8 to 7.4 TA dropped from 90 to 80, CH up from 325 to 350.

 

[mknauss]

of dry acid

Be careful using dry acid in a plaster pool. Sulfate build up in the water can be harmful to the plaster. You are better off using muriatic acid.