pH testing mistakes?

[Household6]

I have the K-2006 test kit.
What are some things I could be doing that would cause my pH test results to be wrong?

I’ve had issues with high pH this year. No idea why. But this morning’s results have produced the most extreme results to date. Yesterday’s test was 7.2. This morning it’s 8.0.

Pump has been running 24/7 for 3+ days.
No rainfall between tests. Did not add water. Robot has not ran since testing yesterday. Nobody was in the pool. No aeration.

Only thing I have done was around 10pm last night I added 2 gallons of 10% LC and dumped out the skimmer baskets (they were relatively clean).

My son did cut the grass yesterday, but very few clippings in the pool as he used the mower with a bagger and as evidenced by small amount of trash in skimmer baskets last night (and I was outside when he was doing it).

What’s going on?!

 

[CraigChing]

Only thing I have done was around 10pm last night I added 2 gallons of 10% LC

The pH test is not accurate at FC levels greater than 10. Posting a full set of tests could help determine if that’s the case.

 

[DanF]

The pH test is not accurate at FC levels greater than 10. Posting a full set of tests could help determine if that’s the case.

Agree.
Since you put 2 gallons of LC in at night, you likely had very little loss in the AM. Plus those color matchers can be difficult to interpret; that's why I chose to get a digital pH tester. Maybe test again in a little while, after your FC comes down. Also you say you've been running your pump 24/7 lately. I have read that the flow from return lines can raise pH, similar to aeration.

 

[Household6]

The pH test is not accurate at FC levels greater than 10. Posting a full set of tests could help determine if that’s the case.

FC was 1.0 for test on Saturday, 3.5 for Sunday. Will link results below.

 

[Household6]

Agree.
Since you put 2 gallons of LC in at night, you likely had very little loss in the AM. Plus those color matchers can be difficult to interpret; that's why I chose to get a digital pH tester. Maybe test again in a little while, after your FC comes down. Also you say you've been running your pump 24/7 lately. I have read that the flow from return lines can raise pH, similar to aeration.

FC was not the issue. Will post link to results below.
I vividly recall the pH colors and I’m certain of the results. But if anything, the 8.0 reading might have been above 8.0.
Prior to this year our pump ran near 24/7.
We got a timer this year. Worked great until a few weeks ago, now it turns on at the appropriate time (midnight) but doesn’t turn off. (Off screw likely just needs to be tweaked. Just haven’t had/made time to play with it.)

 

[Household6]

Recent logs from pool app.

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Test Results 08-23-2020 @ 11:41 AM
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Free Chlorine: 3.5
pH: 8.0
Total Alkalinity: 60

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Chemical Addition 08-22-2020 @ 10:06 PM
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+ 2 Gallons of Bleach

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Test Results 08-22-2020 @ 04:57 PM
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Free Chlorine: 1.0
pH: 7.2
Total Alkalinity: 60
Calcium Hardness: 410
CYA: 40

------------------------------------------
Chemical Addition 08-21-2020 @ 08:54 PM
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+ 2 Gallons of Bleach

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Chemical Addition 08-20-2020 @ 09:56 PM
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+ 32 FluidOunces of Baume31

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Test Results 08-20-2020 @ 07:39 PM
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Free Chlorine: 0.0
pH: 8.1
Total Alkalinity: 60
CYA: 30

------------------------------------------
Notes 08-18-2020 @ 09:25 AM
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PH was off the chart!

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Test Results 08-18-2020 @ 08:22 AM
------------------------------------------
Free Chlorine: 0.0
pH: 9.0
Total Alkalinity: 80
CYA: 30

 

[duraleigh]

The best way I can answer your question is to say that pH simply doesn't fluctuate like that......it just doesn't. What the problem is I have no idea but the most common situation is testing error.

Water is water and your pool water behaves like everyone else's and pH simply does not move in those wild fluctuations. I wish I could help with an explanation but I have no idea what it might be.

 

[PoolNewb2020]

Looking at the logs above, something doesn't add up. On 8/20 PH was 8.1, 32 ounces of acid was added, then on 8/22 PH was tested as 7.2.
Well, 32oz of acid on a 38k gallon pool will only lower PH by 0.2. This kind of change is simply not possible with the amount of acid used.

More concerning to me is all the 0ppm FC readings with your highest at only 3.5ppm. I would address your low FC pronto. For CYA of 40ppm, you should not go below 3ppm FC and should stay between 5ppm and 7ppm.

Don't make the fairly common mistake of chasing numbers while ignoring pretty much the most important parameter which is free chlorine. All your other numbers could be "perfect", but your water could still be green and unsanitary to swim in.

 

[Saturn94]

Make sure you are reading the results immediately after mixing in the drops. As it sits, the sample will darken giving a false high reading (how long this takes seems to depend on FC level).

It’s also good practice to take the sample from the same place every time, away from returns and about elbow deep.

 

[dschlic1]

Poor quality bleach may have an excess of caustic soda which will raise your pH.

 

[Household6]

Looking at the logs above, something doesn't add up. On 8/20 PH was 8.1, 32 ounces of acid was added, then on 8/22 PH was tested as 7.2.
Well, 32oz of acid on a 38k gallon pool will only lower PH by 0.2. This kind of change is simply not possible with the amount of acid used.

More concerning to me is all the 0ppm FC readings with your highest at only 3.5ppm. I would address your low FC pronto. For CYA of 40ppm, you should not go below 3ppm FC and should stay between 5ppm and 7ppm.

Don't make the fairly common mistake of chasing numbers while ignoring pretty much the most important parameter which is free chlorine. All your other numbers could be "perfect", but your water could still be green and unsanitary to swim in.

I agree! That’s part of what’s so bewildering!
Yes, I’m guilty of neglecting to add LC and DO need to change my mindset about consistent keeping it within range. Having said that, water is crystal clear - has been all season.

 

[Household6]

Poor quality bleach may have an excess of caustic soda which will raise your pH.

Hmmmm . . . Husband bought the last batch of LC. I wonder if he checked the date.

 

[Household6]

Make sure you are reading the results immediately after mixing in the drops. As it sits, the sample will darken giving a false high reading (how long this takes seems to depend on FC level).

It’s also good practice to take the sample from the same place every time, away from returns and about elbow deep.

I don’t allow the water sample nor the test results to sit. Always get the water sample from the same place - elbow deep in the middle of the short side on the shallow end.

 

[Household6]

Haven’t added any chems since Monday’s posted results.
Robot ran once Monday for 2 hours.
Son swam for 1 hour Monday afternoon.
Husband for 20 min Monday evening.
This morning’s results pictured.

 

[setsailsoon]

6,

There are lots of different things going on with a pool at any given time. I'd say your results may be due to testing technique, possibly lack of mixing, and possibly bleach quality. Try testing at different 3 different points in the pool like shallow, mid and deep end. Are the results the same? If not how much flow are you getting from the pump? Filter may need to be back washed - check the filter pressure. Looks like pH is reacting in the right direction but just not the right number. This makes me think it may be a mixing issue. The Taylor tests are very accurate and these test results are probably correct or very close. Focus on FC while you figure this out. Shoot for a couple ppm over target and adjust when it gets down to target again. Getting a green pool in the middle of all this would not be fun.

I hope this helps.

Chris

 

[PoolNewb2020]

This may be a reading error/inconsistency, at least that's how it looks to me, there is no 7.9 PH on the scale so there is some interpretation going on or over analyzing/over thinking on OPs part.
Try using 4 drops instead of 5, it may help.
This test is not meant to be super accurate and as long as your PH is in the 7 number range, you do not need to do anything. Once it reaches 8, knock it down to 7.5-7.6 with muriatic acid. Even if it drops a little more or less than expected, it's not a big deal as long as it is in the 7s.

No need to overthink this, especially while neglecting free chlorine levels.

 

[DanF]

This may be a reading error/inconsistency, at least that's how it looks to me, there is no 7.9 PH on the scale so there is some interpretation going on or over analyzing/over thinking on OPs part.
Try using 4 drops instead of 5, it may help.
This test is not meant to be super accurate and as long as your PH is in the 7 number range, you do not need to do anything. Once it reaches 8, knock it down to 7.5-7.6 with muriatic acid. Even if it drops a little more or less than expected, it's not a big deal as long as it is in the 7s.

No need to overthink this, especially while neglecting free chlorine levels.

^That^

 

[mguzzy]

^That^

^That^ -that

 

[Household6]

This may be a reading error/inconsistency, at least that's how it looks to me, there is no 7.9 PH on the scale so there is some interpretation going on or over analyzing/over thinking on OPs part.
Try using 4 drops instead of 5, it may help.
This test is not meant to be super accurate and as long as your PH is in the 7 number range, you do not need to do anything. Once it reaches 8, knock it down to 7.5-7.6 with muriatic acid. Even if it drops a little more or less than expected, it's not a big deal as long as it is in the 7s.

No need to overthink this, especially while neglecting free chlorine levels.

Since when are we not to use a “between“ number for pH?

I’m not sure how my physical testing could be off. I mean, it’s one of the easiest tests ImO. And same way I’ve done it for past years. But any ideas?

Previous years have shown the pH to rarely need adjusting. That’s why I’m so puzzled. Our sweet spot for personal preference is 7.8 and never had issue with keeping it between 7.6 and 7.8 before this year. Now it won’t hold and it goes up quick.

Having said that, I’m pretty sure I figured out the reason for recent large variances from day to day - old bottle of R-0004. Expired 6/2017. <OOPS!> First test this morning showed 7.6. To be sure, I tested it again, but shook the bottle up first (I usually shake all of them. Not sure why I didn’t this time). Sure enough, test came back at 7.9. Third test also showed 7.9.

And just tested again being sure NOT to shake bottle and though not as significant (bottle had only sat for 12 hours) got 7.4. Shook and tested again and got 7.6 (I added 2 cups of MA this morning, so that’s about right).

Now, does the old affect the accuracy when a bottle IS shook? Maybe. I’ll know more after I get a fresh bottle.

Not worried about the FC level. Pool does fine and I’m not going to get caught up on numbers. (Touché?) but because it can’t hurt to keep the FC up for reasons of figuring the ph out, I’ll overcompensate for it and keep it right. (Added 2 gal of 10% this morning. Current read is 3.5. Target is 5. Adding another gallon.

Thanks all for chiming in! I appreciate your time.
No matter the case, I’ll report back after a few days with the new bottle of R-0004.

 

[Household6]

6,

There are lots of different things going on with a pool at any given time. I'd say your results may be due to testing technique, possibly lack of mixing, and possibly bleach quality. Try testing at different 3 different points in the pool like shallow, mid and deep end. Are the results the same? If not how much flow are you getting from the pump? Filter may need to be back washed - check the filter pressure. Looks like pH is reacting in the right direction but just not the right number. This makes me think it may be a mixing issue. The Taylor tests are very accurate and these test results are probably correct or very close. Focus on FC while you figure this out. Shoot for a couple ppm over target and adjust when it gets down to target again. Getting a green pool in the middle of all this would not be fun.

I hope this helps.

Chris

Good ideas, Chris! Thanks for input!
See my response above.