What does acid actually do when it's added to water? And since it "burns through" alkalinity, does that include cyanurate alkalinity? Does acid reduce CYA?
[00:00] - Intro
[00:51] - Researching alkalinity since 2016
[05:27] - CYA contributes to TA, so does acid reduce CYA?
[07:09] - Acid vs. Bicarbonate Reaction
[09:08] - Sodium and Chlorides are Spectator ions
[12:10] - Does acid burn through Cyanurate Alkalinity too?
[15:04] - What about chlorinated isocyanurates?
[17:20] - Closing
192. "Burning Through" Alkalinity and CYA?
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Eric Knight-4: Welcome back everybody to the Rule Your Pool podcast, the only podcast with a production budget equivalent to my target LSI, zero. Anyway, I'm your host Eric Knight. This is episode 192, and I've got to tell you, I received one of the best questions I've ever received since 2019 starting this silly show.
And I got to tell you, this deserves some focus. And I thought I have taught alkalinity and explained it. I know I've explained it in several different ways, and I thought I've really covered it in depth on this show. So honestly, I was looking at other topics. This question kind of punched me right between the eyes, and I am stoked to get into it with you.
If you have ever heard me talk about acid, and I'm quoting if you're not watching, burning through alkalinity, this episode is for you. It's going to go a little bit deep. I'm going to go through some formulas, but hopefully it makes sense to you, and when you're in the backyard, you'll know what's happening when you're pouring that acid into the water.
Let's get into it
[00:00:51] Researching Alkalinity since 2016
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Eric Knight-4: I want to start back in 2016. Now, I had been in the industry for a few years prior to this. I started in actually the HVAC side of things to work on indoor air quality for pools. And then I went to an app startup that I started with one of my assistant coaches, where I learned all these skills like blogging and creating a website and building an app.
I carried forward those skills into Orenda, and now you have the Orenda app and a bunch of research that was done. And one of the things I learned along the way was how to research problems that I didn't understand. But another skill that is not as often talked about was identifying what to write about.
And it surprised me when I got to Orenda. I got to be honest with you. I thought the most Googled topics, so to speak, would be things like algae or green water or, you know, insert common questions here. Chlorine, you know, chloramines. Nope. No, I mean, those are search topics, but nothing even close to the number one topic.
It's going to surprise you. The word was alkalinity.
And I got to thinking like, What? That's a pretty boring subject. Like most homeowners probably aren't looking up alkalinity. Well, you'd be wrong. Because it's on the test kit and people don't really understand what it is. And so I got to thinking like, why would this be such a Googled question? And so I started looking into it. I started reading a lot. And the pool industry really didn't have a good explanation of it. No offense to those who wrote it. It just didn't make a lot of sense. And the best explanation I heard was actually in the IPSSA Basic Training Manual written by the late, great Bob Lowry.
And kudos to Bob. He explained it, I would say the best in the pool industry. But it still really didn't quite register with me what it was. I mean, it was described as a buffering agent that neutralizes acids, and all of that is true. But what does that actually mean? So as I learned and moved forward in the industry, and you have been along with me if you've been listening to this show, I started realizing the CO2 equilibrium.
I learned this from the papers actually provided by onBalance, but it's through the journal, uh, I think it's the Journal of the Swimming Pool and Spa Industry, JSPSI or something. Anyway, if you want to read them, you can go on poolhelp.com. That's the onBalance website. And I learned a lot from a guy named John Wojtowicz. And he wrote a lot of papers, and they were way over my head. In fact, I referenced the LSI formula in a previous episode not too long ago where I showed that formula. And you can find it on the Orenda site or just go to-- just Google them. Honestly, in the era of AI, you'll find it. Super detailed work.
And I kept coming back to it thinking, "All right, I have a goal. I'm going to understand this." Well, as it was explained to me as we were developing the app and we were building out the pH ceiling function, the concept of carbon dioxide kept coming up. Now, carbon dioxide, as we've talked before, is a proxy for your pH. Technically, pH is the potential or the concentration of hydrogen ions.
But, uh, the actual word is potens Hydrogen, or the potential or I should say the power of Hydrogen or the concentration of hydrogen. The problem with Hydrogen is I can't really conceptualize it. I don't know what it looks like. It's just an invisible gas, and I, I just don't really deal with Hydrogen in my day-to-day life.
But because we have bicarbonate alkalinity in our water, that becomes a good proxy because that is what is neutralizing that Hydrogen. So if you have Hydrogen in your water, like hydrogen ions from an acid, for instance, it's going to bind to your alkalinity. That alkalinity, for the most part, is carbonate alkalinity. And therefore CO2, the amount dissolved in the water is going to kind of, well, proxy. It's kind of like an index fund. If you're doing an index fund in the stock market, it's following the trends of the market very quickly. So the more dissolved CO2 in the water, the higher the concentration of Hydrogen, therefore the more acidic the water, and the lower the pH.
And as CO2 leaves, this is where it becomes relatable to us because we've all had a beer go flat, or a soda go flat where you can see the bubbles leaving. That concept is true because of Henry's Law. Any gas dissolved in a liquid must equalize with the same gas above the liquid. This is why your carbonated drink goes flat, but your pool is going flat too, because you're more carbonated in the pool than the air above the pool until they equalize.
When your pool, air quotes, "goes flat," you can't lose more CO2, and when you can't lose more CO2, your pH can't go up anymore because you're in equilibrium. That's what we call the pH ceiling.
[00:05:27] CYA contributes to TA, so does acid reduce CYA?
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Eric Knight-4: So I've said six minutes of all of that just to get into what this question is. So I want to read this question for you. I'm going to shift windows over here. This comes from Zachary. Zachary says, "Hey, Eric. I was just catching up on some podcasts and listened to the episode on adjusted carbonate alkalinity. It made me wonder if you have high CYA, as many pools I see in Southern California do, would adding acid regularly to bring down pH and alkalinity burn off the CYA?
If one-third of your alkalinity is cyanurate, wouldn't that mean it's getting taken out alongside the carbonate alkalinity? I'm sure I'm wrong, but I'm just not sure how. Thanks for everything you do for us service guys. Zach."
Zach, thank you so much for the email. There is a bit of a typo, misnomer. I want to correct that. I think I know what you mean. You said, uh, in the email, you said, "If one-third of your alkalinity is cyanurate..." Okay, that's not quite. So it's actually one-third of your CYA parts per million is cyanurate. It's not one-third of your alkalinity. It does contribute to your alkalinity, but you don't take your total alkalinity and divide it by three. It's how much CYA you have. Take a third of that roughly. It is pH dependent, and the Orenda Calculator is super precise, but for the rule of thumb, a third of your CYA is going to be cyanurate ion.
That contributes to your total alkalinity, and when you're calculating the carbonate or corrected or adjusted alkalinity, all three of those are the same thing. You just subtract that cyanurate from it. But here's the crux of the question. If I add acid to the pool, is it going to remove CYA?
No, it's not. And there's a difference between escaping, or I should say, an off-gassing event, which is what happens with bicarbonate alkalinity, and an equilibrium event. But in order to explain that, and I will come back to that in a moment, I want to show my screen here.
[00:07:09] Acid vs. Bicarbonate Reaction
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Eric Knight-4: And for those of you listening, I'm going to do my best to describe it. I first want to explain what I mean when I say burning through alkalinity. No, it's not a fire, but it's a good visual because when I ask questions in classes, and I've taught a lot of classes, I try to get people to conceptualize why CO2 is so important and why the pH ceiling is so reliable.
One of the things that I have made it my mission in this industry to do is help pool pros and homeowners alike, anybody who treats water, understand the natural state of water, understand the physics that are actually controlling it. Because you and I don't control water. We never did. We never will. Physics does. And if we don't understand those physics, then you're just going to keep throwing chemicals and maybe expensive equipment, trying to manipulate it to try to beat it into submission, and it just doesn't work. That's the problem. It just doesn't work.
So on the screen here, I have written out three formulas and sort of an explainer here. So I'm going to take my time. And I'm just going to explain what I mean by air quote, "burning through alkalinity."
When I add an acid, and the most common acid in this case is going to be muriatic acid, which is 31.45% or less hydrochloric acid. That's HCl. Now, what I've done with this formula here is I've color-coded the chlorides, the Cl, in blue, and the sodiums in orange. So if I add chemicals to the pool, let's say I add sodium bicarbonate, also known as baking soda, or for the homeowners out there, alkalinity up. It's a white powder, sodium bicarbonate.
If I have those chemicals interact with each other directly, you're going to get a big fizzing reaction. Now, if you put them in the water, it's a little bit different. That'll be the next formula. But let's just say we interacted them directly.
Hydrochloric acid plus sodium bicarbonate yields sodium chloride, which is table salt, NaCl, plus water plus CO2, carbon dioxide. And that CO2 is a gas. But that's not the actual reaction happening in a pool because these chemicals are in the water. Well, they undergo hydrolysis. And hydrolysis changes things because if I add sodium bicarbonate to water, the sodium separates from the bicarbonate.
[00:09:08] Sodium and Chlorides are Spectator ions
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Eric Knight-4: The sodium becomes what is called a bystander, or more scientifically correct, a spectator ion. Even in a salt cell, the sodium kind of just passes through. Yes, it is part of sodium hydroxide, but it separates from the hydroxide. And this is why salt cells are mistakenly thought to raise the pH from chemistry, but they don't actually raise the pH from chemistry. They do create sodium hydroxide, and that is a high pH. But they also create chlorine gas, which is a pure acid. And after that salt cell, they neutralize each other to effectively a 7.0 pH. So it's actually a perfectly neutral chlorine production.
But the turbulence creates the off-gassing of carbon dioxide, and that's what raises the pH in a saltwater pool. So it's not chemistry, it's physics that raises the pH in a saltwater pool. All of this is very well documented. I've talked about it ad nauseam. You can go back to previous episodes.
But the point here is sodium and chlorides. Now, I should say chlorides meaning the depleted form of chlorine. A chloride is a Cl minus. It's not a Cl2. It's not an active chlorine. It can't kill. It can't oxidize. It is in its final oxidation state. It's a inert ion. They are spectator ions. They are in this reaction, and they are on both sides of the reaction, but they really don't do anything consequential. So that's why I color-coded them, so you can see, oh, there's a chloride, and there's a sodium on the left.
And then, well, they combine into salt on the right, but it's still one sodium and one chloride. So they're pretty much neutral. So the focus of the reaction is actually the hydrogen, which is the acid combining with the bicarbonate, which is HCO3-.
But that's not really the reaction that's happening Because when I put these products in a pool, they undergo hydrolysis, meaning they dissolve in water. So the sodium separates, the chlorides separate. So let's just take them out into their little component pieces, and that's the middle equation here.
So I have a hydrogen ion, aqueous, plus a chloride ion, aqueous, plus a sodium ion, aqueous, and bicarbonate ion, aqueous. Then that yields a sodium aqueous, a chloride aqueous, water, a liquid, and CO2, a gas.
So now I've got hydrogen meeting bicarbonate. In other words, acid neutralizing on bicarbonate alkalinity. When I say this burns through alkalinity, here's what I mean. It creates water and CO2. But there's actually an intermediary in there, isn't there? Because if I add hydrogen to bicarbonate, I don't just immediately jump to H2O plus CO2 and the CO2 off gases. That eventually happens. That is the net result. But it actually creates carbonic acid. Carbonic acid is H2CO3.
So if you look at the very bottom of the screen, I know I'm jumping around. If you look at the very bottom of the screen, see if you can see my mouse, H plus HCO3, all I've done is taken out the, uh, spectator chlorides and sodium here. Hydrogen plus bicarbonate creates carbonic acid, H2CO3, which then splits into water and CO2, which off gases.
The carbonic acid pulls the pH down. Hmm, word vomit. I'm 13 minutes into this according to this, and, uh, yeah, I hope I haven't lost you yet.
[00:12:10] Does Acid Burn through Cyanurate Alkalinity too?
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Eric Knight-4: Now, in the next section, this is going to make more sense. Why, why Eric? Why are you going through all this nonsense so that we can talk about CYA? Because this is super important. What it's actually doing is it is getting rid of some of this material. It's not just reverting it into something else. The acid is converting bicarbonate into salt, water, and a gas that leaves.
That's CO2 off gases. Remember Henry's Law? It leaves. So you can't just replace that alkalinity. It doesn't come back. It went into the air. In a different form, but it went into the air. So by getting rid of that CO2, your alkalinity goes down. And this is why when you put acid in the pool to lower your pH, your alkalinity also goes down.
As a bit of an aside, if you are a commercial pool operator, and thank you for listening to this, I know we have quite a few of you now. If you are injecting carbon dioxide instead of acid, you'll notice your alkalinity doesn't go down. In fact, if you're using liquid chlorine or cal hypo, because you're not using acid, those chlorines have a little bit of an excess hydroxide that actually increases your alkalinity over time.
Your alkalinity goes up. It's very strange. But acid is what brings alkalinity down, and it does not come back up on its own. If it does rise on its own, you had to have a source of alkalinity. In many cases, that's a hydroxide coming out of a plaster surface, or somebody added a hypochlorite chlorine and didn't neutralize it with acid, blah, blah, blah. That's a different episode for a different day.
Your alkalinity does not naturally rise on its own. The pH does because of the loss of CO2. That's basically the distinction of what I'm trying to say. So when I say acid burns through alkalinity, it actually gets rid of it. It off gases into the air in a different form.
You are left behind with salt or sodium and chloride ions and water. And that's what you had in your pool to begin with. So it is a net reduction in alkalinity.
Now, to the next page. To get to Zach's question, does acid reduce cyanuric acid? The short answer, no. Here's why. There's a huge difference between escape and equilibrium.
What I mean by that is what we just discussed was an escape. CO2 left. It off gassed. It's gone. Cyanurate doesn't do that. So if I add a hydrogen, this time I've made the hydrogens pink, so they're very easy to see. If I add a hydrogen to a cyanurate ion, that's C3H2N3O3-, and I made the minus pink because that is relevant to where the H is going to go.
I have two hydrogens and a negative valence in cyanurate ion because it's a conjugate base. It's a conjugate base of cyanuric acid. It's missing a hydrogen. And that negative attracts that hydrogen, and you get this reversible reaction where you go C3H3 because you just added the hydrogen to the H2, N3O3, and it's balanced.
Boom, you got cyanuric acid. So this is just an equilibrium reaction of cyanurate ion, your other words cyanurate alkalinity. Which is the conjugate base of, on the other side of the reaction, cyanuric acid. So when I add acid, I don't get rid of CYA. I'm adding acid. All I do is I move the hydrogen.
[00:15:04] What about chlorinated isocyanurates?
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Eric Knight-4: I move the hydrogen over. Then the question becomes, okay, well, that's great if it's just CYA, but what about chlorinated CYA? Like, what about CYA that's bound to chlorine? A couple things on that. The first thing is in a pool with, say, 50 CYA or 30 to 50 CYA on a residential pool, when you're comparing that to two to five parts per million free chlorine, the actual number of molecules measured in moles, CYA massively outnumbers chlorine.
Now, don't mistake me here. That's not necessarily a bad thing until you get over stabilized, and that's why we always recommend staying below 50 parts per million on CYA on a residential pool and below 15 parts per million on a commercial pool. Yes, you are outnumbered, but it depends on how much interference is actually in the water. And if you have too much CYA, it really slows down your chlorine quite a bit.
But the point is most of your CYA doesn't have chlorine on it. So technically, yes, chlorinated isocyanurates like dichlor, they do actually have some buffering capacity, but it's a drop in the bucket. It's like not even measurable in a pool.
And that's because you just have so little of it compared to the rest of your CYA, which does contribute to your total alkalinity in a meaningful way. So the second reaction here on the page is that a chlorinated isocyanurate, in this case dichlor, still has a negative valence, and it can still attract a hydrogen.
So it is a base, and it will neutralize some. But instead of, like, fundamentally changing what's happening and certainly not off-gassing something, it's just kind of parking the hydrogen to become cyanuric acid once again. Or in this case dichlor. So as we move down to the second equation, now we have a chlorinated isocyanurate, in this case dichloroisocyanurate, and that is a negative valence. So it's still a base, and it can still attract the hydrogen. The difference is there's no escape mechanism. You're not off-gassing a portion of cyanuric acid like you would off-gas CO2 with bicarbonate alkalinity.
So you're just parking the hydrogen there, and as that pH rises naturally due to the off-gassing of CO2, Henry's law, pH ceiling, all that, that hydrogen just goes right back into the water. Now, you are welcome to check my work on this. This comes straight out of John Wojtowicz. In fact, everything from this comes from John Wojtowicz.
He has several papers. This one's from 1999. He has another one from 1995, and if I scroll back up to the first part, that comes from 1993.
[00:17:20] Closing
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Eric Knight-4: So all that is to say, in summary, I, I bet Kathryn is long asleep by now. When you put acid into a pool, in a stabilized pool anyway, you have at least two types of alkalinity. You have your carbonate alkalinity, which is mostly bicarbonate ions, and you have your cyanurate alkalinity. Roughly one-third of your CYA is cyanurate alkalinity. So you can neutralize these things with acid. But the difference is cyanurate becomes cyanuric acid, but it doesn't go anywhere. And then as the pH rises, that hydrogen jumps back off, and, it goes right back into its own equilibrium.
Whereas with carbonate alkalinity, you're burning through it, air quotes, my term. You're burning through it because the CO2 leaves. That's kind of like the air quotes, smoke of the reaction. So you actually permanently reduce that until you replenish it. So if you put acid in, you're going to reduce your total alkalinity.
The CYA isn't going anywhere. The cyanurate isn't, but the carbonate alkalinity is. I hope this helps. It's probably clear as mud.
But, um, yeah, just a great question. Honestly, the, the quality of questions that I'm getting at ruleyourpool@gmail.com is astounding. I've got several others, and I told you in, I think the last episode or the one before, I don't know how to answer a lot of them.
I'm still waiting to hear back. I have reached out to some pretty high-powered or well-known intellectuals that you may recognize. You know, I'm just-- I guess I don't have... Yeah, I think the threshold is you have to have over 300 listeners for them to pay attention to you. So tell your friends and see if you come back to this show after this one.
Hopefully, I don't lose too many subscribers. Oh, by the way, there are some classes with Watershape University that are soon to be available online, and we also have some scheduled for the fall. There will be an advanced construction class. If you are going for your IWI, this is a requirement for wellness, and this will actually be at the MIZU Cover Con in October. We're going to have one of our instructors, Ben, teaching our three-day construction school in the greater Houston area in late September in Katy, Texas. Uh, we've got several other classes available and, and, uh, the education vacation is being planned right now. If you want to learn up and you want to get into the pool construction, design, engineering, any of those spaces, go to watershape.org, see what's there.
Putting a lot of effort into those classes to try to get them there. And of course, the service track that I keep teasing is just, uh, it's a huge project. But when it comes out, you'll see it's worth it. Anyway, thanks for listening to the Rule Your Pool podcast. This has been episode 192, and I hope to see you back next week. Tell your friends. Thanks.