pH dropped MUCH lower than Pool Math predicted?

[mgtfp]

Here it is with CYA of 300 ... recommending 117oz

You can't enter parameter combinations into PoolMath that aren't chemically possible, PoolMath is not clever enough to realise that. If you enter TA 100, then changing CYA will not have an impact on the calculation, as PoolMath simply takes the TA value for the MA estimation.

As Marty already pointed out, with CYA 300, the CYA-Alkalinity alone would already be about 100. With CO2 being in equilibrium with atmospheric CO2, TA needed to be at least about 150 to be in equilibrium at pH 8.3. 117oz of MA would get you down to 7.8 in this scenario.

 

[Stoopalini]

I just did some calculations with Chem Geek's spreadsheet, which should be more accurate than PoolMath when it gets to larger pH changes.

When entering parameters as in your logs, then the PoolMath calculation is actually not far off, those 117oz should have lowered pH from 8.3 to 7.6.

I suspect that your borates are lower than you assumed. With BOR 20, pH would drop to 6.9.

The TA drop to about 60 makes sense, it matches the 117oz of MA, and the TA reduction is more or less independent from the BOR level.

How are you testing your borates level?

As recommended, make bigger adjustments in smaller steps.

Edit:
Just saw that you are using strips for Borates. They are OK for a rough estimation. How does your colour blindness affect reading these strips?

There is a titration test possible with a few chemicals added (Mannitol sweetener and a pH-Indicator) on top of standard Taylor reagents. But you need to be able to compare blue-shades to get the endpoint right. It might be possible to use your pH-meter instead of the pH-Indicator.

It is described here:

New borate drop test at piscines-apollo vs. test strip

Thanks, SunnyBlues. You have been reading and learning a LONG time to remember all those experts. Thanks for your testimonial.

www.troublefreepool.com

This makes sense. Yes, my colorblindess makes it where I cannot read strips, so I have my wife read them for me. I've gotten to the point where I just need her for the FC test on a regular basis. I also need her for the salt titrate test, the borate test (using strips), and the metals tests (also using strips ... LaMotte 2994) when I run those a couple of times a season.

This season my CYA went from 80 at the start, down to 50/60 or so somehow ... and I had to bring it back up some weeks ago. We haven't received a lot of rain, so it makes me wonder if maybe I have a leak somewhere? If I do, the borates being reduced would make sense, but it would have to be a significant leak I think to drain 7000 gallons and reduce the borates by 1/2. Unless borates can be lost by some other mechanism other than water leaving the pool?

Thanks for the info on the titrate test for borates. I'll certainly check that out. And will probably do a bucket test as well, just to see if I'm losing water somehow.

 

[mgtfp]

Unless borates can be lost by some other mechanism other than water leaving the pool?

Nah, not really. Water leaving the pool is the only way.

Have you tested your salt level?

 

[Stoopalini]

Last time I tested the salt was May, but I do look at what the IC40 reports and it hasn't really fluctuated. I can test it again though, and it should give me a good indication if I'm losing water somehow. Good point ...

 

[mgtfp]

That may be interesting for you:

My borates are testing very high on the Taylor test strips. Do the strips expire or go bad? The test is coming out at 100, which is the highest on the test, so who knows how high it might actually be if the strip is accurate? The house water is testing at 50. I have NO idea if house water should be testing at any or not. (We did add a water softener recently, but the pool was filled last year way before we added it. I dont know if that affects borates either).

Sounds like those strips don't last forever. Putting your and JenfromNC's info together, it looks to me that those strips tend to show borate levels too high when going bad.

 

[RickRude]

I've just noticed for myself a discrepancy between pH projection and Effects of Adding. I do not use borates.

I assume pH is more accurate since it requests TA and current pH. But FWIW, adding according to the pH projection page has never gotten me to the target.

 

[mgtfp]

Yes, the Effects of Adding calculation doesn't seem to consider the current TA and BOR levels. It also doesn't consider the start-pH, which also has an influence (the pH scale is a log-scale, so a delta of e.g 0.4 between 7.2 and 7.6 is not the same in terms of H⁺ concentration as between 7.6 and 8.0, and the buffering capabilities of carbonates, CYA and borates each change with pH). For other chemicals, the Effects of Adding works quite well, but pH-changes are more complex to calculate and not as easy to approximate from lookup tables, and require multiple input-parameters that the Effects GUI doesn't offer.

The acid-amount suggestions from the overview-page are more accurate as they consider TA and BOR. But they are still approximations, so it is recommended to do larger acid additions in multiple steps. Not just because of approximation errors, but (and that is I think the bigger risk) also because errors in your TA and BOR measurements (and that includes taking months old TA/BOR measurements assuming they wouldn't change) could result in overshooting (as in the OP's case).

 

[mknauss]

I've just noticed for myself a discrepancy between pH projection and Effects of Adding.

Read the NOTE at the bottom of the Effects Of Adding Chemicals for pH. The results are only accurate with a very tight range of chemistry parameters.

 

[Stoopalini]

That may be interesting for you:

Sounds like those strips don't last forever. Putting your and JenfromNC's info together, it looks to me that those strips tend to show borate levels too high when going bad.

I ordered the materials I need to do a drop based borates test, and am just waiting for the deliveries. So I'll check it when they all arrive. My guess is you are right, in that the dip strips are no longer reading accurately and my borates are lower.

Back in March, at the beginning of the season, my borates tested at 20ppm using the strips; but that was after losing about 1/2 the pool water due to a snapped pressure relief valve at the top of my filter housing. So I expected the borates to be way down. I added 20lbs of boric acid then, and it raised it up to 50ppm per the strips. Ever since then, they've tested at 50ppm and we haven't had enough rain to account for overflow.

So if the drop based test does show 20ppm (or similar), I may have a leak somewhere.

Tomorrow I plan to test the pH change again using the MA I have, as well as run a bucket test just to rule out a leak. Then when the rest of the materials arrive, I'll also do a drop test for borates.

 

[mgtfp]

I ordered the materials I need to do a drop based borates test, and am just waiting for the deliveries. So I'll check it when they all arrive. My guess is you are right, in that the dip strips are no longer reading accurately and my borates are lower.

Back in March, at the beginning of the season, my borates tested at 20ppm using the strips; but that was after losing about 1/2 the pool water due to a snapped pressure relief valve at the top of my filter housing. So I expected the borates to be way down. I added 20lbs of boric acid then, and it raised it up to 50ppm per the strips. Ever since then, they've tested at 50ppm and we haven't had enough rain to account for overflow.

So if the drop based test does show 20ppm (or similar), I may have a leak somewhere.

Tomorrow I plan to test the pH change again using the MA I have, as well as run a bucket test just to rule out a leak. Then when the rest of the materials arrive, I'll also do a drop test for borates.

I think the borate drop test is quite fun. The tricky bit is getting the blue shade right with adding 1-2 drops of R-0010 after turning it yellow with R-0009, and then remembering that shade of blue as the endpoint for the actual titration after adding the Mannitol and then R-0010 as titrating reagent. I usually take a photo with my phone before adding the Mannitol and put the phone with the photo as a reference next to the test tube.

The Speedstir is really helpful for this test, because the test tube is quite full (at least the one I use) and hard to swirl manually.

 

[RickRude]

Read the NOTE at the bottom of the Effects Of Adding Chemicals for pH. The results are only accurate with a very tight range of chemistry parameters.

Sure, I've read the note. But it's reasonable for a user of the app to expect the calculations to be based on the same logic and take into account the current state of your pool chemistry based on your latest logs. Furthermore, as I said, adding according to the pH correction page has never gotten me to the target level anyways.

 

[Stoopalini]

I think the borate drop test is quite fun. The tricky bit is getting the blue shade right with adding 1-2 drops of R-0010 after turning it yellow with R-0009, and then remembering that shade of blue as the endpoint for the actual titration after adding the Mannitol and then R-0010 as titrating reagent. I usually take a photo with my phone before adding the Mannitol and put the phone with the photo as a reference next to the test tube.

The Speedstir is really helpful for this test, because the test tube is quite full (at least the one I use) and hard to swirl manually.

I’m colorblind, so was planning to use my PH60 meter to check the pH after adding the 1-2 drops of R-0010 to turn it blue, and then using the meter at the end of the test to determine when the same pH is reached again.

Yep, I’m sure I’ll be glad to have my speedstir during this test

 

[Stoopalini]

Sure, I've read the note. But it's reasonable for a user of the app to expect the calculations to be based on the same logic and take into account the current state of your pool chemistry based on your latest logs. Furthermore, as I said, adding according to the pH correction page has never gotten me to the target level anyways.

Are you sure your pool is 21,500 gallons exactly? I used my water meter to get the exact gallons of my pool when I originally filled it, which is how I know it’s 14,060 gallons. The recommendations from pool Math have always been spot on for me, almost eerily spot on … this is the only time in the past 2 years where it hasn’t hit the target almost exactly.

 

[Stoopalini]

Today I checked the chemistry ... pH reading 8.25 with TA between 70 and 80, so let's call it 75.

Pool Math suggested 49oz of 20* MA to reduce pH to 8.0 (assuming 50ppm borates), so I added 49oz.

Later in the day, I retested and the pH had dropped to 7.68 with TA reading a solid 70.

So either my borate strips are bad, or the MA I'm using is stronger than it's supposed to be.

The test strip bottle has an expiration date of Oct 2022 ... but of course, they could still be bad. I tested some tap water with them, and it was a solid 0ppm.



Here is a pic of the pool water test:



The family tells me this is a solid 50ppm reading, but I cannot tell myself.

I wish the BTB had a faster ship time, but it hasn't even shipped yet and has an estimated delivery window of Aug 16 - Sep 1.

I read through the Borate drop based test thread, and it looks like maybe I can use the pH meter to do some testing until I get the BTB. My understanding is ... I would follow the procedure to lower the pH to 6.0 (to convert any boron to broic acid I believe?), then raise the pH back up to some target (from the thread, 8.3 seems like a decent target), then add the mannitol, followed by R-0010 drops to bring the pH back to the 8.3 target, counting the number of drops to determine borate count. Not sure if this is accurate though, as a lot of chemistry talk in that thread goes over my head.

If the borates are indeed less than 50ppm, then it means I've lost some water somehow. I'll try and do a bucket test over the next 24 hours, just to check.

 

[RickRude]

Are you sure your pool is 21,500 gallons exactly? I used my water meter to get the exact gallons of my pool when I originally filled it, which is how I know it’s 14,060 gallons. The recommendations from pool Math have always been spot on for me, almost eerily spot on … this is the only time in the past 2 years where it hasn’t hit the target almost exactly.

No, but I took a fairly detailed survey to get to 21500. Before that I'd been operating under my old pool guy's estimate of 18K, and I'd always wind up short of my chlorine targets. After revising up to 21.5 after my survey, my chlorine is spot on. Besides this doesn't have anything to do w/ PoolMath giving different estimates on the two different pages.

 

[Stoopalini]

No, but I took a fairly detailed survey to get to 21500. Before that I'd been operating under my old pool guy's estimate of 18K, and I'd always wind up short of my chlorine targets. After revising up to 21.5 after my survey, my chlorine is spot on. Besides this doesn't have anything to do w/ PoolMath giving different estimates on the two different pages.

I was asking that because you stated this:

Furthermore, as I said, adding according to the pH correction page has never gotten me to the target level anyways.

If your gallons are off, then the pH will never hit the target by adding what Pool Math suggests. There's obviously something off in what you're doing, as most other folks have accurate pH results after adding what pool math suggests ... The targets for me has always been spot on for everything, including pH ... except for the instance I'm dealing with now. But what I'm dealing with isn't a Pool Math problem, or I would have always had this issue.

 

[Stoopalini]

The autofill has been turned off along with the waterfall being temporarily disabled, and the bucket test is underway

 

[Stoopalini]

I received all the stuff needed for the drop based borate test today, except for the BTB. So I went ahead and ran two tests with the pH meter, to see what results I get.

1st test:

1. Collected a 50ml water sample
2. Added 2 drops of R-0007 to neutralize the chlorine
3. Used R-0009 to reduce the pH with a target of 6.0
   1. It ended up at 6.03, and I stopped there
4. Added 2 drops of R-0010, which raised the pH up to 8.16
5. Added two level 1/8 tsp of Mannitol .. pH dropped into the 5's (I neglected to write this number down)
6. Added drops of R-0010 to raise the pH back up with a target of 8.16
   1. At 7 drops, it was in the high 7s, very close to 8, for pH
   2. The 8th drop sent the pH up over 9

So if this is a valid way to run this, 7 drops x 4 is around 28ppm borates


2nd test:

1. Collected another 50ml water sample
2. Added 2 drops of R-0007 to neutralize the chlorine
3. Used R-0009 to reduce the pH with a target of 6.0
   1. 8 drops had it in the low to mid 6's, so I added a 9th drop, which took it to 5.87
4. Added 2 drops of R-0010, which raised the pH up into 7s.
   1. I added a 3rd drop, since I was using 8.3 as a good target, and it took the pH to 8.58
5. Added two level 1/8 tsp of Mannitol .. pH dropped into the 5's (I neglected to write this number down)
6. Added drops of R-0010 to raise the pH back up with a target of 8.58
   1. At 8 drops, it was in the low 8s
   2. The 9th drop sent the pH up over 10

So again, if this is a valid way to run the test, 8 drops x 4 is around 32ppm borates

So it appears I'm somewhere between 28 - 32 ppm borates, not 50. I do have boric acid here, ready to go, but I won't add any until I get the BTB delivered and can run the test again with my wife watching the colors. If the results of that also show 28-32 ppm, then maybe using a pH meter is a good alternative way to do this test for colorblind folks.

 

[mgtfp]

Looking good. But yes, maybe wait for the BTB and do the test once with your wife with BTB and the PH60 at the same time. Like that you can correlate the colour descriptions with a pH-value.

I agree that "straw yellow" should be pH 6.0. But for the high point the description says

This is the hard part - you want to get the indicator dye to just turn blue, like a baby-blue and not go all the way back to a deeper blue.

I think this should be closer to 7.5-7.6 than >8:



I don't think the exact pH matters too much, important is that it's the same again at the end of the titration as before the Mannitol addition. Staying at pale blue rather than going to the end of the scale allows a more precise match, but with a pH-meter it shouldn't matter as you can measure 7.6 with the same precision as 8.2. But with the BTB you wouldn't know where exactly you are once it's dark blue.

But I see where you were coming from, two drops just got you to 8.16. I usually stop at 1 drop (with a 40ml sample, don't have a larger tube), after two drops it gets already quite dark blue. But I think the third drop in the second test might have been too much.



But we'll done. Good to see that your tests seem to align pretty much with what we were expecting from theory. And good on ya for showing others with colour blindness a way to do titrations. I tried the TA-test once out of curiosity with my pH60, but never did the borates test with it.

 

[JoyfulNoise]

It’s very hard to do a titration using a pH meter and the R-0010 drops that we have available. If you have ever done an acid-base titration before you know that what you’re dealing with is an S curve where there is a slow increase in pH with added base and then a very rapid rise followed by a very long plateau. It is actually the volume of base added at the midpoint of the rapid rise that determines the titration. If you had very detailed and precise data, then the first derivative of the S curve will yield a peak (maximum slope) at the midpoint value.

So, with the BTB indicator, the pale baby blue is sort of the midpoint value you’re looking for. But it is easy to overshoot with the R-0010. It would be better if it were slightly less concentrated than it is.