Mystery pH spike

[Rollercoastr]

I've been known to brag about how well I can predict test results. Apparently, my pool overheard me...

On Thursday:

FC: 3
CC: < .5
TA: 90
pH: 7.5
CH: 375
CYA: 30
Tmp: 88º

The FC of 3 is intentional. I've been keeping it on the lower end lately. (indoor pool w/ a light bather load)

I had a guest over and we lounged in the pool for several hours. She mentioned that knowing she would be swimming, she hadn't applied lotion that day.

I dosed the pool with some LC and covered the pool.

No swimming on Friday.

I had some more guests over on Saturday. Before we suited-up, I decided to test FC and use my new pH tester. FC was at 2. I expected that and wanted to take it to about 4 anyway. Then I fired-up my new pH tester and it read 8.8. I was really frustrated, because I found the calibration process fussy and it took many attempts to get it where I wanted it. I had an email to Lee half-written in my head when I decided to grab the OTO block. I've never seen it that purple! The tester was definitely in the neighborhood, and very possibly spot-on.

I wondered if something had messed with the TA, so I tested it and it came back the same it's been for about year now: 90.

I added enough acid to bring it 7.8 We swam, but the water had that "dull" look that's been mentioned here so many times in the context of unbalanced pH. I took some pics of my guests beautiful dogs standing next to the pool. I don't think it's my imagination that the dullness even shows in the pics.

Sure enough, pH read 8.1 after the swim.

My pool gets basically no aeration. I didn't add anything unusual to the pool. I'm baffled!

 

[mknauss]

Swimming aerates.

How long ago had you OTO tested the pH prior to the recent test? And as far as I know the color block does not go to 8.8

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I think I missed your timeline.

You state the pH was 7.5 on Thursday, tested with OTO, and by Saturday it was 8.8? Only if you had added borax.

 

[Rollercoastr]

Yep. I received and calibrated the tester on Wednesday. pH was 7.8 by the tester and OTO. I added acid to reach 7.5, which it still was when I tested before swimming the following day.

I have a box of borax that I bought before I read enough about it. It's several years old now, and still sealed!

 

[mknauss]

I would be sure to test after running the pump for awhile or get a sample from another area of the pool before reacting to that big a jump in pH without chemical being added. It is not naturally possible.

 

[Rollercoastr]

Gratuitous pic of these beautiful pups... (am I right!?) but in the foreground, "dull" water.

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I would be sure to test after running the pump for awhile or get a sample from another area of the pool before reacting to that big a jump in pH without chemical being added. It is not naturally possible.

I'm with ya. That's why I didn't add acid to get below the high 7's. It's just so odd to me that the look of the water, OTO and the tester all agreed...