Does Liquid Chlorine Raise pH?

On June 28th, if you recall, we discussed with pool/spa water chemistry expert Richard Falk the impact of sodium hypochlorite on pH in our piece titled “Liquid Chlorine Raises pH, or Does it?“. Richard explained that the pH rise folks typically experience in swimming pools comes from the outgassing of carbon dioxide, and not from hypochlorites. In part 2 of this 2-part series, we pose the same question to leading industry scientist Robert Lowry.

Photo Credit: A Grande Choice Pool & Spa, Inc in Englewood, FL

Sodium Hypochlorite (NaOCl) is one of the more popular methods of chlorinating swimming pool water in both commercial and residential applications. When NaOCl (liquid chlorine) is added to water HOCl, Na+, and OH– is formed. However, what happens after the hypochlorous acid (HOCl) is used up (either due to UV from sunlight, or as the chlorine sanitizes and disinfects) is a common topic for debate among pool operators. Chemically, the HOCl becomes HCl (hydrochloric acid) in the process – no one is arguing this. The controversy is regarding whether the amount of acid (HCl) produced is enough to counter balance the initial increase in pH the dose had generated.

To clarify, I had reached out to both Richard Falk and leading industry scientist Robert Lowry for their thoughts on the chemical reaction. Initially seeking a brief explanation in a “paragraph”, what I received in return was so much more:

So if I am using liquid chlorine and it does not raise pH, what is causing the pH to go up all the time?

Robert W. Lowry (AKA: The Water Coach)

According to chemical consultant, author, and pool/spa water chemistry expert Robert Lowry (AKA: The Water Coach), “The short answer is that you have the wrong or too high TA (total alkalinity). I usually recommend 90 ppm as a starting Target TA. If at this target the pH is drifting up, then change the Target to 10 ppm less or 80 ppm. And if that doesn’t work, try 70 ppm TA. If on the other hand your pH is drifting low, raise the Target TA to 100 ppm. Again, change in increments of 10 ppm until pH is stable.”

 

Robert Lowry went on to explain: The problem is that when the TA level is too high there is a lot of outgassing of carbon dioxide (CO2) that causes the pH to rise. You may also have a lot of splashing and aeration in the pool that accelerates such outgassing. If you were to let the TA drop to 80 ppm or even a little lower, you will find that the rate of pH rise will slow, especially if you target a pH of 7.5. If you find that a lower TA level helps, then you may need to raise the Calcium Hardness (CH) level a little bit to compensate for the saturation index to protect plaster surfaces.

Aeration of the water and turbulence will raise the pH theoretically until the amount of carbon dioxide in the water is in equilibrium with the air. This pH of equilibrium then depends on the TA level. At roughly 200 ppm TA (ignoring CYA), the pH could theoretically rise to 8.77, but in practice you will see it on go up to about 8.5 or less.

You can see that pools are way over-carbonated. We are just fortunate that the rate of outgassing is relatively slow and that even aeration has a limited effect of speeding it up. If you want to run your aeration and turbulence-causing systems all the time, then you will likely be adding acid all of the time. You might consider using a timer for aeration and turbulence causing devices so that they run when people are around to enjoy them and not when they are at work.

 

The double arrows indicate that things are in equilibrium and go back and forth to maintain equilibrium. So if you raise or lower any of these items, everything else shifts to keep the equilibrium.

Removing CO2 raises pH and adding CO2 lowers pH.

 

Shout out to TJ Palmer (TJ the Pool Guy) for sending me spiraling in this direction.

Rudy’s Thoughts: Something that must be considered is that in a continuous feed system, one will experience the following: NaOCl becomes HOCl, Na+, and OH–; HOCl (Hypochlorous acid) eventually becomes HCl (Hydrochloric acid) which lowers pH. However, the amount of HCl formed is only in a quantity sufficient enough to negate that from which it came from. As the chlorine level is being continuously replenished by the addition of sodium hypochlorite, the pH level remains a consistent elevated high contingent upon the continued dosing. A cyclical process where the HCl formed, at best, can merely keep up (Like Lucille Ball at the conveyor belt). So, still a net zero change to pH, but the continuous addition maintaining a constant high pH until the addition of the NaOCl (sodium hypochlorite) should cease.

Robert’s Response: You are correct that if you start with no chlorine level and you add hypochlorite then the addition will raise the pH and while it will get lowered as it is consumed or used, additional hypochlorite will raise it again so that starting from 0 ppm and getting to and maintaining 3 ppm results in an elevation of pH that is not lowered unless you explicitly adjust the pH.  But that is exactly what is done.  Once one achieves the FC level desired, say, 3.0 ppm, then one adjusts or lowers the pH.  From that point forward, there is little change in pH from the hypochlorite itself except for the excess lye in it and that rise typically only shows up some in high bather-load pools using lots of chlorine per day. The excess lye in hypochlorite is typically 0.03%. This is very little lye. Considering that a gallon of sodium hypochlorite 12.5% is 128 fl and weighs 9.66 lbs per gallon, there is about 0.046 oz (1.4 grams) of lye. I would doubt that this amount of lye would have any effect on pH in 15,000 gallons.

So, again, if the pH is going up using continuous hypochlorite feed, the problem is high (wrong) TA, high aeration or turbulence. Start with a Target TA of 90 ppm and adjust up or down in 10 ppm increments until pH remains stable depending on whether the pH is drifting up or down.

Robert Lowry is the Author of many swimming pool industry publications. “Pool Chemistry For Service Pros” is one of his most recent. The handbook offers science based, logical, easy method of maintaining pool water chemistry using only basic chemicals – liquid chlorine or bleach, muriatic acid, bicarb, borate and air. You only have to make a few adjustments to what you are already doing to realize the benefits.

Don’t forget to throw us some STARS if you liked it:

[ratings]

Or, please feel free to leave us a comment below:

 


0

4 thoughts on “Does Liquid Chlorine Raise pH?”

  1. According to my testing, you can’t keep a “constant” FC level reading in a pool. The sun UV and sanitizing is constantly changing those readings through out the day and then you have to add chlorine to replenish daily so that would mean the PH fluctuates too according to this article. I have a HASA liquid Chlorine feeder that dispenses chlorine at night while the pump runs on high speed (not an electronic dose feeder). I test in the morning and that’s when the FC levels are the highest naturally and as the day wears on the sun etc lowers the FC chlorine levels about 4 ppm seems to be the variance. When I test in the morning, the PH is high which I adjust with dry acid and also lowers TA a bit too (they seem to rise and fall together although PH makes bigger adjustments). I can’t see the feeder being an issue because it wouldn’t be any different than if I poured chlorine in manually every day too. Your article etc on this subject is confusing because to me it says adding chlorine doesn’t effect PH and then it says it does. I pretty much see a pattern that it does and I do test several hours after chlorine is added. Also my city water ph is 7.8 too so when I add more water to the pool if I’m trying to maintain a lower PH, it’s a fight. So what I’m gathering PH changes throughout the day too as the chlorine level lowers, so maybe I need to take my tests in the evening instead. I just need to know how much to adjust the flow on the chlorine feeder to the pool at night so it’s 3-5 ppm the next early evening when we use the pool and maintain the pool ph so I’m not constantly adding acid.

    The technique for lowering TA by lowering and raising PH to stabilize PH is something I don’t see practiced even by pool service companies. I am experiencing TA on high side too so I’ll try to get that down just wish there was an easier method that didn’t require adding a butch of chemicals too.

    0
    1. Hello Darlene, thank you for reading! You hit a lot of good points here. 1st, Addressing your statement “Your article etc on this subject is confusing because to me it says adding chlorine doesn’t effect PH and then it says it does.”: You have nailed it! The purpose of the article was to address the reason why some folks see a raise in pH when using sodium hypochlorite and others do not. Industry chem expert, Robert Lowry, explains that Total Alkalinity is the culprit.

      Water Chem expert, Richard Falk, offers another possible reason in this one: https://cpoclass.com/liquid-chlorine-raises-ph/

      To address your thoughts in why the TA & pH both fall with the addition of acid: https://cpoclass.com/acid-column-slug/

      0
  2. Forgive the rambling, but I’ve got to get this out. I Absolutely love this discussion and love that David has brought on a true pool-care icon; Robert (Bob) Lowry; who, along with Richard Falk, aka Chem Geek, may one day get the industry to start using chemistry for pool care advice and slow down the nonsense that’s being taught today by the industry. David needs to go out next and get Richard Falk to talk to us, but if Richard comes on, we’ll really have to put on our chemistry thinking caps, because he can get pretty deep in to the chemistry formulas and charts without even realizing that he’s over our heads. Below is a link with more of Bob’s info about all things TA, PH and saturation index related from an article he wrote in to for a journalist in 2018. I’ve also put a link in to what Richard is doing nowadays, which could result in significant changes to the industry, but, like I said, put on your thinking cap with Richard’s report to the CMAHC. This is a technical report and it’s been done to try to effect a change in the recommendations for free chlorine levels and also relate free chlorine to the cya level, which is not the recommendation in the industry today where we manage them separately, which is, of course, a farce. I couldn’t understand all of what Richard’s group was saying in their summary, but it looks like that, in general, they did some work to determine that at least one pathogen that is released from sloughed fecal matter (I think that means normal release from a human in a pool; not an accident) causing infection in another at 1.5 meters away, can be cut in half by simply increasing the FC level by twice it’s current recommended level at 90 ppm cya. This report did not deal with algae or other organics in pools; just three pathogens; and one of those three had a significant finding. Bob’s interview is mostly this same topic; about using bleach and how that does NOT increase PH in pools; at least not in the end.

    I’ve been trying to nail this down for a few months now just for understanding my own pool. See, this year I over shot my CYA goal and I’ve been sitting just above 60 on cya all season. I use the TFPC methodology for pool care, which means that I must maintain my FC at a minimum 7.5% of my CYA level at all times. So at 60, my minimum is 5, as you always round up, and this means my target each day is 2-4 ppm above that minimum (7-9), and once you hit middle of summer, most users will have to tend towards that upper target level (mine is 8), as there is more UV during the middle of summer and therefore, chlorine breakdown by UV is higher this time of year; and with TFPC you dose daily with liquid chlorine or bleach, which is really all bleach; just different strengths. My CYA level this year makes it hard for me to get what TFPC calls an accurate PH reading, because, over at TFPC, they say that to get a good reading on a PH drop test, your FC must be below 10; otherwise, the result is invalid. But in practice, I’m finding anything above 6 gives me a higher PH reading than what I see when FC is below 6. But then that got me thinking…Is it the test that is it the test result above FC 6 that’s bad, or is it more that the PH is actually high until the extra dose of bleach does it’s work and turns in to acid and then the PH goes back down? And I think that might matter. I asked that question on the forum, and only one person attempted to answer that question with a chemistry-style answer, and that person basically said that it’s the latter; that the PH does go up and then back down just like we’ve talked about on here. I got other answers, but they were more about the actual test kit that I owned and suggested that I get a Taylor kit instead of the one I was using and with a Taylor kit, it would be accurate up to FC 10; other kits can be accurate only up to FC 3. But when I got the Taylor kit, I could tell it was the exact same manufactured-kit as my Clorox kit, and so I’m inclined to believe that what is actually happening, especially after David’s interview with Bob, and the after reading of the linked article below by Bob, that what is really going on is that my PH is fluctuating from dose to dose using my bleach; it’s higher more often this year, because I’m dosing FC higher than a normal year where I’d have CYA from 30-40, which is just another reason I like CYA closer to the lower limit. So, to think even deeper then, since we now have an idea that by using bleach at least, our PH is going high, then back down each time we dose with it, “what then” is the proper or “best” PH level when the FC is back down; just before re dosing for the next day? Should it be a little low when it’s down, so that it’s average is in range? I’m not sure. Right now, mine has dropped once again, just a tad, down to 7.1. This is where it went when I first added too much stabilizer at season’s beginning. I had left it at 7.1 for many weeks and finally decided to add borax and raise it to 7.3. I hit the target exactly and had been at 7.3 when FC was down for about three or four weeks; but now recently, it’s showing back down to 7.1, and based on everything I’ve learned through experience and via the smartest pool people I know, I may end up having to barely raise my TA level to steady the PH out just a little more if I want it to sit a little higher when the FC is down. However, since my PH seems to stick at 7.1 and my FC is averaging about 7 in a 24 hour period and my PH is obviously averaging higher than 7.1; maybe I should leave it alone. But just to add one more wrinkle, the TFPC pool math calculator says my CSI is -.95, and I think that Bob might have something to say about that; that I’m probably running to corrosive with my water even as my liner is vinyl. Anyway, I’m going to order one of Bob’s books; the best one to explain all of this that his website recommends, and also include some practical stuff to help me do my own balancing; maybe I’ll add borates and CH as that may allow me to raise my TA somewhat and keep PH steady, because my TA is 50, and that too is adding to my corrosive issue, if in fact, it is an issue.

    https://www.cmahc.org/documents/CMAHC_Ad_Hoc_Committee_Report_on_Stabilizer_Use._WAHC_2017-10-16_FINAL.pdf

    https://www.poolspanews.com/how-to/maintenance/chemical-guru-robert-lowry-explains-recent-changes-to-his-chemistry-method_o

    0
  3. When the FIRST sentence of a comment is ‘Forgive the rambling’… Wow! I think your remark may be longer than the article. ? That said, I agree. Both men are brilliant and I have been lucky enough to collab with both to one degree or another over the years. My only question on your comment – Who the heck is David? ??‍♂️

    0

Leave a Reply

Your email address will not be published. Required fields are marked *