Did Polyquat jack up my pH... or is it interfering with R-0004/T-9056??

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Sampo

Sampo

Gold Supporter
Aug 19, 2022
77
Southeast PA
Pool Size
34000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-60 Plus
Hi TFP friends! I need some help.

For background, I'm in the process of closing for the first time by myself 🥳. My chemistry had been balanced and very predictable for months (thanks to TFP). After doing a "soft close" on Saturday (solid cover on, but pump still running), I'd passed my OCLT, had FC perfect at 1/2 SLAM level, and was just waiting a few more days to get my temps solidly below 60F before winterizing. But then I added Polyquat... and my pH results went crazy! Here are more details of what happened:

  • Prior full panel (10/12/24 13:52 pm): FC=12.0, CC=0.5, pH=7.5, TA=70, CH=400, CYA=60, NaCl=3,200, Temp=60F, CSI=-0.48.
  • Last reliable pH (10/13/24 10:15 am): pH=7.6. (also passed OCLT)
  • Added 40 oz Polyquat 60% (10/13/24 10:29 am). Nothing else added. Cover had been on. SWG off for a while.
  • Next pH test (10/13/24 17:34 pm): pH= "iridescent magenta" -- off the scale (best guess = 8.4?). Whoa! 😲 Test repeated: same result.
  • Added ~0.25 gal 31.45% HCl (10/13/24 21:11 pm).

At this point, I started searching through TFP forums. I found this discussion which suggested that the result might be an artifact -- a false reading from the drop test. In fact, I'd seen that same "iridescent magenta" color in my comparator once before: last year after my PB closed my pool (they also used Polyquat, although I previously thought that they really did shoot up my pH by using a weird borate-containing winter float :cautious:).

Since I wanted an independent check of the pH reading with any other methodology than my Taylor test, I just went to Leslie's for the first time in about a year (I know, I know -- I'm sorry! 🫣). Their results: pH=8.1 (ok, maybe...), and TA=5 (false for sure! My TA has been rock-solid stable at 70).
Funny aside: their tech had never heard of Polyquat (lol)... but he did predictably tell me that my phosphates (1325 ppb) were "algae food!". But I digress.​

After coming home, I've rerun my Taylor test several times (I'm using R-0004/T-9056). The end result is always that same "iridescent magenta" color, suggesting that my pH is 8.0++ (picture below). But after several runs, I've noticed something interesting: the sample first flashes orange (pH=7.4-7.6 range) for the briefest of moments... before quickly turning magenta -- only for about a second as I'm shaking the comparator.

Based on the prior TFP discussion I've linked above, my current best guess is that the orange flash is real and that the magenta color is false: that my pH is really ~7.5 (implying a CSI=-0.48)... rather than being absurdly high at around 8.2+ (implying a CSI=+0.39). That would fit based on where my pH had been before the Polyquat and my panic-addition of the muriatic acid above -- based on what I intuitively know about pH levels in my pool.

But is there a way to know for sure? Or does it even matter? The pH is sure to rise in the winter, so I'd love to start it off right.

Thanks for your thoughts, and CYA later!
Sampo

Polyquat did this.JPG
 
Polyquat and linear quat algaecides are organic compounds that are known to cause interference's with certain color indicating reagents like pH indicators (as you have seen and others have reported the purple results). Adjust the pH before adding Polyquat 60 and there is no reason to test pH after adding it.
 
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I would not worry about it.

I get my pH and FC right for close and then add Polyquat. Once the Polyquat is added I don't check the chemistry during the closing.
 
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Interesting. It just feels so antithetical to everything that I've learned about TFP methods: we check a starting level using a reliable test, then add chemicals with intention, and finally recheck levels to be sure that the addition had the expected effect. That is, I'm so used to checking levels before/after chemicals -- particularly with something that I haven't used before (Polyquat) that verifying the pH afterwards was just habit. But your approach makes sense in this one context, given the interference you mention.
 
Also since there is talk about chlorine oxidizing the polyquat chains into shorter strands, I was academically curious to see if the FC dropped after the Polyquat addition (it didn't -- although the CC became slightly pinker, but still <=0.5).
 
Sampo said:
Also since there is talk about chlorine oxidizing the polyquat chains into shorter strands, I was academically curious to see if the FC dropped after the Polyquat addition (it didn't -- although the CC became slightly pinker, but still <=0.5).
Click to expand...

That does not happen overnight. The Polyquat will interact with the chlorine over the long term.
 
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I know this thread is inactive, but I've got some interesting follow-up that I'd like to share in case others see this discussion in the future:

We had some unexpectedly warm weather after I had covered my pool -- so I've kept my pump running much longer than I had originally planned. Thus, I've been able to track my chemistry to see what happened after this rash Polyquat addition.

In brief, the pH artifact from the Polyquat only persisted for a few days. Even after the first 2 days, the sample would briefly flash to the "correct" pH value before turning purple -- in fact, I think I'll coin the term "Polyquat purple" to describe this artifact! By about a week, things were back to normal.

In more detail:
  • I had added Polyquat 60% at a rate of 11.8 oz per 10kGal (40 oz in 34,000 Gal pool).
  • For the first 24h, both the drop based pH tests and a "reference test" at Leslie's were completely unreliable/uninterpretable. They falsely suggested that my pH was off-the-charts high (Polyquat purple). In retrospect, it wasn't high.
  • By 48h, my R-0004/T-9056 test started returning back towards normal: after adding the Phenol and shaking the comparator, the color would stay on the [presumed] correct value for about 3 seconds -- before quickly drifting to Polyquat purple.
  • By 72h+, the sample was staying at the [presumed] correct pH color/value for much longer.
  • By 6 days, my drop test was functioning as usual.

I hope that this info helps someone else in the future. If you're reading this thread after adding Polyquat and then testing your pH right afterwards: DON'T PANIC! 🤪(y) Your high pH reading isn't real -- it's just Polyquat purple! Don't add acid! Either forget the reading and close your pool -- or if you absolutely need to follow the pH before fully closing, just wait a few days for your test to normalize. And as usual, the pool store tests won't help the situation.

CYA later!

Sampo
 
To put it in simplest terms without getting too much into the chemistry weeds, yes this a well known interference. Phenol red is an organic compound that exists as a negatively charged molecule in neutral and alkaline solutions. Polyquat-60 is a long chained quaternary ammonium polymeric compound that exists as a positively charged molecule in neutral and alkaline solutions. When you mix the two together, the positively charged quat links up with the negatively charged phenol red and basically “locks” the indicator into its purple/magenta “high pH” state. This is why the solution turns a vibrant purple color. You would normally only see that color from phenol red when the pH is higher than 8.4.

As you have determined, you can either wait a few days to retest when the interference is gone or you can get a pH meter and use that to test pH since the PQ-60 will have no effect on a standard pH meter.
 
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Wow! Super cool to get a response from another TFP legend. While I have your expertise, can I ask a follow-up, @JoyfulNoise ? Why would the Polyquat interference/artifact disappear after a few days? As others have pointed out, the Polyquat doesn't degrade very fast. So I'd imagine the Polyquat is just as much of a cation a few days later. Why does the Phenol test start to work then?
 

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Polyquat doesn’t last that long especially under highly oxidative conditions like a closing SLAM. It’s half life is a few days at best.

The details of the chemistry get pretty “in the weeds” but the color change has to do with the two phenol groups and their aromatic resonance structure (color typically comes from ring like molecules with delocalized resonance electron bonding). When you add functional groups to these types of aromatic ring structures, it changes the way the delocalized π-bonded electrons absorb light. Because the energies lie in the visible part of the spectrum, subtle changes to the structure of the molecule can shift the absorbed and emitted photon wavelengths all the way from the near-IR/red end to the blue/UV end of the spectrum. So as the polyquat breaks down, the changes in color absorption can vary by quite a lot. It may be that the longer, more intact PQ60 locks in the deeper purple color while shorter chain quats do not.

You are also dealing with a water sample that has high FC which can cause the phenol red dye to convert to chlorophenol red which has a much lower pKa. That causes the color transition to happen at a lower pH which results in a purple color at neutral pH and higher. So between the PQ60 and the high FC, the phenol red isn’t going to give good results.
 
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Thank you! It's been 20+ years since my organic chemistry classes, but I think I can still roughly follow the outline of this thoughtful explanation. I think the bottom line for me is that the Polyquat is getting chopped into pieces far faster than I expected -- and despite the manufacturer's claims that it still works just fine in that form, that does raise a bit of doubt as to how much benefit it can possibly give over the duration of the winter (if it did, why wouldn't it come in a shorter chain form to start?). Given the extra pH measurement headaches, I'll think about skipping it next year. Anyway, I really appreciate your expertise, and you having taken the time to explain. Many thanks to you and the other legends of TFP!
 
Sampo said:
Thank you! It's been 20+ years since my organic chemistry classes, but I think I can still roughly follow the outline of this thoughtful explanation. I think the bottom line for me is that the Polyquat is getting chopped into pieces far faster than I expected -- and despite the manufacturer's claims that it still works just fine in that form, that does raise a bit of doubt as to how much benefit it can possibly give over the duration of the winter (if it did, why wouldn't it come in a shorter chain form to start?). Given the extra pH measurement headaches, I'll think about skipping it next year. Anyway, I really appreciate your expertise, and you having taken the time to explain. Many thanks to you and the other legends of TFP!
Click to expand...

PQ-60 is a branched quat algaecide as opposed to a linear molecule. So it will last a lot longer, relatively speaking, than a linear quat. One benefit of the PQ-60 is that it doesn’t cause much foaming on initial treatment like the linear quats do, and so that is more aesthetically appealing for pool use. Using it at closing time is just a little bit of extra insurance in case there’s a freak weather pattern and the water warms a bit. Temperature is really the biggest factor and so if you open and close right around the 60F mark, the pool water will generally stay clean and be easy to deal with no matter the use of PQ60 or not. As you have figured out, aside from the annoying interference issue, it’s really not harming anything.
 
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Polyquat 60 and PH

I am closing and added 1 quart of Polyquat 60 to my 16x32 inground pool. A couple of days later I checked the PH and it has gone off the scale to the high side. I added 14 drops of R5 acid demand to get it back to about 7.8. Nothing else has changed and the FC is 7.5. I have searched the forum...
www.troublefreepool.com www.troublefreepool.com
 
mickey4paws said:
My experience with Polyquat 60: I have only used it once, several years ago at closing. I added it and some time after I took a PH test. The test turned a very dark purplish magenta color, and this was an immediate test, as I never let my samples sit after testing. It freaked me out as the day before my PH was in normal range, probably 7.5. I just figured it must be some kind of reaction with the reagent and not a true indication of PH. I haven't used Polyquat 60 since at closing since it really didn't make a difference on how my pool was in the spring at opening.
Click to expand...
Here is a report that attributes the pH color change to polyquat.

What references can point to polyquat interference with the pH test?

I think that we would see a lot more reports of pH interference if it was a real phenomenon.
 

does polyquat 60 raise pH?

I have been doing everything just as I always have. My pH has been pretty consistent. There was a big rain last night and today. I drained some out and checked the chemicals. My CL as still at 11, but my pH was over 8. I added the drops for the acid demand test and just don't think something is...
www.troublefreepool.com www.troublefreepool.com

Polyquat

Does anyone know if adding polyquat raises the ph. This morning ph was good. 7.6. Added a little more acid target of 7.5. Now this afternoon ph is above 8.0. After adding polyquat this morning. Nothing else added.
www.troublefreepool.com www.troublefreepool.com

Maybe some anecdotal evidence for a pH interference with polyquat, but I think that it is not a proven fact.

Maybe if the level is super high due to poor mixing.
 
Northern cannonball said:
Today I added algaecide and let the pump run about 8 hours. I just tested my FC and PH and my FC dropped a little as expected, however my PH shot up to 8.
Click to expand...
Northern cannonball said:
FC is 10ppm. It was 12.5 before I added the algaecide
Click to expand...
DeptOfMeteors said:
I asked the pool store's advice and one of their recommendations was to put 500mL of algaecide over 24 hours. When I test for pH, and I first drop the reagent in the container, it turns yellow which appears make the pH 7.2, but it's a much darker yellow than the guide. By the time I get upstairs to ask my wife for a second opinion, it turns to a dark magenta, indicating well above 8. No, it's not a matter of changing lighting conditions. When I return to the scene where I started the test, it stays the high pH colour. I've run the test twice.
The FC is a little higher than normal but only about 7ppm, so my best guess is that the algaecide is interfering w/the R-0014.
Click to expand...
There are some reports of pH interference with algaecide, so maybe it is a thing, but it seems unlikely to me.

When chlorine combines with phenol red, it becomes chlorophenol red.

Phenol red C19H14O5S + OCl- + HOCl --> Chlorophenol red C19H12Cl2O5S + H2O + OH-.

Chlorophenol red has a similar color range to phenol red but the colors happen at a lower pH as shown in the chart below.

The pH indicator (phenol red) has reducing agents that should reduce the chlorine at up to 10 ppm.

So, either the reducing agents in the phenol red are compromised or the FC is higher than you think.

1730645929343.png
 

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