Terry Arko joins Eric to talk about the pH impact of each chlorine product used in swimming pools. What is actually going on when these chlorine products dissolve in water?
00:00 - Introduction
01:12 - Old habits and beliefs about chlorine and acid
07:04 - Liquid chlorine (sodium hypochlorite)
11:07 - Our bodies produce HOCl too
12:13 - HOCl will become HCl (aka muriatic acid)
16:00 - Cal hypo (calcium hypochlorite)
21:30 - Sodium Dichlor (dichloro-s-triazinetrione)
21:46 - Trichlor (tricoloro-s-triazinetrione)
26:36 - Saltwater chlorine generators (SWG)
30:43 - Chlorine gas (Cl2)
33:16 - Closing
135. Chlorine's pH impact in swimming pools
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[00:00:00] Eric Knight: Hey everybody, welcome back to the Rule Your Pool podcast. I'm your host Eric Knight with Orenda and Hasa, and this is episode 135. And with me today is our special guest who has been on here several times and several times more in the future. Terry Arko.
[00:00:13] Terry Arko: Good morning. Uh, I don't think it's morning where you are anymore, but it is still morning here in gloomy Seattle where I am this morning.
[00:00:21] Eric Knight: I am across the country and it is already afternoon for me. And we are just enjoying the joys of Microsoft. Trying to get your camera to work and synchronize with this, but we're doing this one on video. And the reason we're doing this one on video is we've received a lot of questions about how chlorine impacts the pH of swimming pools, like various chlorine types, and you're the expert on chlorine.
[00:00:42] And the reason I want it on video is we've got the Bob Lowry book right here, and I know you've been teaching the Pool Chemistry Training Institute, the PCTI, you know this book better than anyone except for Bob. Rest in Peace. And we're going to go through this and we're going to talk about what these chlorines actually do to pH in a pool and why.
[00:01:00] Terry Arko: I know there's still a lot of people in the pool industry that have questions about this, so I think it's a good subject to tackle.
[00:01:06] Eric Knight: All right, let's do it. Episode 135 of the Rule Your Pool podcast. Let's go.
[00:01:12]
Old habits and beliefs about chlorine and acid
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[00:01:12] Eric Knight: One of the things that I was taught when I first came into the industry is you have to add a certain amount of muriatic acid to offset the high pH of liquid chlorine. Let's just quickly go over that habit, Terry. What were you taught back in the day? Because you've been doing this a lot longer than I have. And then what has that habit evolved into? Like, what are people saying nowadays?
[00:01:54] Terry Arko: Yeah, so I started in the pool industry in the late seventies cleaning pools. And basically it was like, Hey, they hired me, I was like 21 years old, something, you know. And we're going to take you out, you're going to ride with the veteran pro. He's going to show you how to treat a pool.
[00:02:11] Well, one of the first things they told me when I got to a pool and it was getting to chemicals, and this was not even, had nothing to do with even testing pH, the chlorine, anything. It was just that you're going to put a gallon of this liquid in let's say a gallon per 10,000 gallons. And for every gallon of this liquid in, you have to put a quart of acid in. That's what I was told.
[00:02:30] Eric Knight: A quart?!
[00:02:31] Terry Arko: Of acid per per gallon. That's what I was told. I can remember early on because I'm always an inquisitive guy, if somebody tells me to do something, I want to know why. Um, and so I asked why. And I was told don't ask why, just do it. It's the way it's been done. Seriously. I, you know,
[00:02:49] Eric Knight: That's so representative of our industry, isn't it? I mean, how often are people today told, oh, Don't question it. Don't question this. Just do it. Oh my gosh.
[00:02:59] Terry Arko: later on, I know somebody came along and told me, well the reason you've got to do that is because this liquid chlorine has a very high pH. And when you put it in the water, your pH is going to go way up high. And if you don't put any acid in, that's going to screw up your water chemistry. And so you got to balance it out with the acid. And I accepted that. I was like, okay, well that's an answer I can accept. I didn't take that much further. And so I did pools for years that way.
[00:03:22] Eric Knight: What were you seeing? Were you noticing any issues over those years? Or, or were the plasters better?
[00:03:28] Terry Arko: you know, I think the main thing that I noticed, and it was mainly because of a couple of things. You know, I, I sort of had, uh, two things going against me. And that was I was in Southern California, and Southern California was a huge trichlor market. And basically service at that time was you either had a trichlor chlorinator in line, or you had a floater in the pool, and you kept that thing full of trichlor tablets. And when you came and serviced the pool, you did a shock or whatever you wanted to call it with that gallon per 10,000 or whatever it was of liquid. And because everyone told you, you added more acid.
[00:04:07] So, Orenda talks a lot about the whole Henry's law, and the pH always wants to go up. Well, I never had that problem, and the reason I never had that problem was because I had trichlor, which was just continually lowering my pH and my alkalinity. Then I would put some liquid in there. But then I was adding acid as well. So my pHs were always below the 7.4. They were more in the 7.3, 7.2 area. Maybe now and then they'd go up to 7.5, 7.6 on their own because they were trying to reach the ceiling, you know?
[00:04:37] But acid was just continually going in there, pulling down the alkalinity, pulling down the pH. Which I was something I wasn't aware of for a long time until later I began to learn and learn and learn about what was really going on. And then the big revelation to me was learning how acidic trichlor tablets were. And just, what that was doing alone.
[00:04:58] So, yeah, it was a learning process and I did figure it out over time. Um. Fortunately, I would say because I was in Southern California and the water at that time was so hard coming out of the source, I didn't have a lot of destructive, uh, situations going on as far as corrosion or, or surface etching and that kind of thing.
[00:05:19] Eric Knight: Well, that's good. And back then, believe it or not, in plaster, they used to put asbestos in it to strengthen it, so it was a lot more robust. But generally speaking, based on what you're telling me, that water was probably neutralizing itself against that cement in a negative way. But that cement would've been raising the pH while the trichlor was lowering it. And so it probably stayed pretty stable is what it sounds like.
[00:05:41] Terry Arko: Yeah. Um, whether, whether, whether I knew what I was doing or not, it just, I was fortunate, I guess .
[00:05:48] Eric Knight: So let's talk a little bit about what was actually going on. Because coincidence is not the same as causality. And when we speak to customers, you've been a part of the classes as well, Terry. I'm sure you've had more questions than I have. This habit of having to add acid after liquid chlorine. It has really been pervasive in the industry.
[00:06:06] And of course, we're a part of a company that manufactures both. You can actually manufacture acid as part of the chlor alkali process of creating liquid chlorine. So they are very similar, but believe it or not, chlorine, when it dissolves in water, actually produces its own hydrochloric acid. And of course, Terry, what's another name for hydrochloric acid?
[00:06:26] Terry Arko: Muriatic acid.
[00:06:27] Eric Knight: Exactly right. This is what's actually going on in your water. And I'm really glad to have Terry here to explain it.
[00:06:33] We're about to go through each of the popular chlorine products that are used in the swimming pool business. We'll start with liquid chlorine, then we'll go to cal hypo, calcium hypochlorite, and then we'll go to dichlor and trichlor. And then we're going to talk about salt chlorine generators. And we're going to end on chlorine gas.
[00:06:50] And Terry, back in your day, chlorine gas was actually used. It's outlawed in most states now, but we want to talk about it because that is elemental chlorine. That is what everything is derived on, and we really want to talk about what that actually did in water. You ready to go?
[00:07:03] Terry Arko: Yeah. Let's go.
Liquid Chlorine (sodium hypochlorite)
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[00:07:04] Eric Knight: Okay. Let's start with the Bob Lowry book. In fact, if you have this and you've taken PCTI, it's called pool Chemistry for Residential Pools by Robert Lowry. And I am going to be starting on page 131. If you are following along at home.
[00:07:21] He says on here we're talking about neutralizing the high pH of liquid chlorine. So what basically happens is when you add liquid chlorine to a pool, it goes in there and creates a few reactions. And I actually have it on my screen, my second monitor here. It's, uh, sodium hypochlorite goes into water to create hypochlorous acid, that's HOCl, plus sodium and a hydroxide. Those combine and you get sodium hydroxide.
[00:07:45] Terry Arko: Yes. that's that's correct. Sodium hydroxide is a very strong base. So that's an immediate reaction.
[00:07:52] Eric Knight: And base means high pH. It's alkaline. Okay. So you get a weak acid, which is the active form of chlorine hypochlorous acid, and you get a very strong base. So in the short term, it temporarily raises the pH of the pool. Correct?
[00:08:07] Terry Arko: Yes. that's the first immediate reaction from adding sodium hypochlorite.
[00:08:12] Eric Knight: So the habit came, well, it's got such a high pH, we have to add acid. Now, you were told to add a quart of acid. When I got into the industry in 2016, I was told to add 16 ounces, which is half of what you were told. Do you think that's even necessary now knowing what we know today?
[00:08:30] Terry Arko: Absolutely not. Especially in an outdoor pool with a lot of UV sunlight.
[00:08:35] Eric Knight: there would be an exception to this, and I do want to clarify. If you are going to show up to a pool that has already a high pH, that maybe your pH ceiling is too high. For instance, you have an alkalinity in a liquid chlorine pool, over a hundred, and we've talked about this ad nauseum, but your pH ceiling is maybe over 8.3. It might cloud up the water if you add liquid chlorine to a pool that's already at 8.3, wouldn't it?
[00:09:00] Terry Arko: Yeah. And that would be even more so if they also had a high calcium level along with that. You would cloud the water up.
[00:09:07] Eric Knight: and that's because it's forcing an LSI violation. The high pH is forcing calcium carbonate out of solution. That's why it temporarily clouds. Now this is nothing like adding soda ash or cal hypo to it, which really visibly clouds, but it does cloud until it, you know, disperses and then it kind of goes away.
[00:09:23] If you're going to reduce the pH, the proper practice is to actually reduce the pH before you put the chlorine and separate it by a few minutes. Because the last thing you want to do is pour chlorine on top of where you just poured acid. Why is that, Terry?
[00:09:37] Terry Arko: Because you will basically create a very harmful gas. Yeah.
[00:09:42] Eric Knight: In a pool, it's diluted pretty quickly. But if you were to pour them together in a bucket, you would create a very harmful gas
[00:09:48] Terry Arko: Right.
[00:09:48] Eric Knight: called mustard gas.
[00:09:49] Terry Arko: Mustard gas. It's what they used in World War One to kill people. So.
[00:09:52] Eric Knight: So don't do that. Uh. You're going to dilute, dilute, dilute, dilute dilute your acid if you are doing this. And it's based on the pool's pH, not based on the chlorine. You'll lower the pH of the pool and then you will add your shock several minutes later. Maybe test your water in between or something. Do something else. Go check the equipment. Just give yourself a structural barrier between when you add the acid and when you add the chlorine. Fair enough?
[00:10:16] Terry Arko: Absolutely correct.
[00:10:18] Eric Knight: Okay, we've got this chlorine in there. It temporarily has a high pH. Now that we've created HOCl and sodium hydroxide, we now need to look at what happens to that HOCl. What does HOCl do, Terry? What's its primary purpose in water?
[00:10:32] Terry Arko: The primary reason you're adding chlorine to the pool is to disinfect, and that's what HOCl does. It's the 99% kill agent that's being produced from chlorine, uh, and water. And the hydrolysis of water on chlorine is initially the HOCl, which is the killing agent. That's what you want.
[00:10:50] Eric Knight: And it doesn't matter which type of chlorine product you use, whether it's liquid chlorine or salt chlorine generator, cal hypo, chlorine gas, or any of them will create HOCl. And HOCl specifically is the best algaecide, it is the best germicide. It is the safest, most natural disinfectant that we could put in water.
Our bodies produce HOCl too
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[00:11:07] Eric Knight: And fun fact, I was looking into this. Our white blood cells, when they kill germs and viruses in our bodies, our white blood cells produce a certain chemical to do that killing, Terry. What chemical might that be?
[00:11:20] Terry Arko: HOCl.
[00:11:21] Eric Knight: That's exactly right. And I got to thinking about it. I said, man, that's crazy. Our white blood cells produce chlorine in our own body. Look it up. I might not have believed it if it was on something like Reddit or a social media meme or something. But it was like WebMD and multiple sources online are all saying this. And I got to thinking well over 80% of our body is water, and we consume salt. Sodium chloride. So we get the chlorides from salt.
[00:11:45] Terry Arko: On the medical end, there are a lot of companies that actually produce straight HOCl, uh, using electrolyzed water and salt. I know a company here in Washington State, they do it and they use it for skincare and for different medical situations. It's just straight pure HOCl. Um, HOCl of itself is very safe.
[00:12:04] It can be taken internally sometimes at certain percents and it can be put on your skin and so forth to disinfect and to keep things, you know, just very clean.
HOCl will become HCl (aka muriatic acid)
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[00:12:13] Eric Knight: Wow. I didn't even know that. Okay, so what happens once you have chlorine in the water is it's going to kill or it's going to oxidize, or it's going to get broken down by sunlight. And it doesn't matter which happens to it because either way that HOCl becomes HCl.
[00:12:30] So if it's killing or oxidizing, it is taking an electron from something and it's swapping its oxygen. So HOCl loses its O and it becomes HCl, hydrochloric acid. Now here's the catch. The amount of hydrochloric acid produced is almost almost identical to the amount of sodium hydroxide produced.
[00:12:52] It's not quite, it's a very small percentage short, but generally speaking, it's negligible, uh, because what this HOCl has produced, that acid, hydrochloric acid, also called muriatic acid, is going to neutralize those hydroxides. And so effectively liquid chlorine is pH neutral once it kills or oxidizes or breaks down in sunlight.
[00:13:15] Do I have all that correct?
[00:13:17] Terry Arko: Yep. That's, uh, pretty much what we call an equilibrium reaction. And as you said, the HCl may be slightly a little less than the sodium hydroxide percentage, but it's very close and it's close enough to where you're going to have pretty much an equilibrium reaction. And so the pH is going to basically neutralize out.
[00:13:39] Eric Knight: and that gap while we're here. That gap, I discussed this a few episodes ago. I was talking about alkalinity's complicated relationship with chlorine is the name of the podcast episode. And I noticed on my pool, because I wasn't adding any acid for the whole summer, I kept my pH at pH ceiling to try to prove a point.
[00:13:56] Because I wasn't adding acid, but I was adding liquid chlorine every week, my alkalinity, in spite of the dilution, always stayed between 50 and 60. What was happening was that little amount of excess hydroxide that HCl did not quite neutralize, accumulated over time, and it contributed to my total alkalinity. This is really noticeable on swimming pools that use carbon dioxide for pH reduction.
[00:14:20] I know a lot of big universities and waterparks, they inject CO2 instead of acid, and they notice their alkalinity climbs. And the higher the alkalinity climbs, of course, because of the carbonate alkalinity equilibrium, the faster you have to feed more CO2. And your alkalinity just goes up and up and up and up and up.
[00:14:38] But it's not because of the CO2, it's because you're not using acid.
[00:14:42] Terry Arko: Yes.
[00:14:44] Eric Knight: Terry, anything you want to add to that?
[00:14:45] Terry Arko: That's absolutely correct. And the thing that we find with liquid chlorine, whenever somebody talks to me or contacts me about pH problems necessarily, and they, they're using liquid, so they tend to think that's the suspect is the liquid. Then what we do is we check a little more on their water chemistry, maybe LSI even and so forth. But we find they're running a high alkalinity to begin with.
[00:15:08] What we see happening is the high alkalinity is pulling the pH up. It's not the addition of the liquid chlorine that's doing that.
[00:15:15] Eric Knight: Correct. I actually have that here. And you could go to poolchemistrytraininginstitute.com/why-ph-rises-if-not-from-liquid-chlorine. And you're exactly right, that high alkalinity drives the pH ceiling. It drives how carbonated your beer is, so to speak. It's how carbonated your water is relative to the air above it.
[00:15:33] The more carbonated you are, the higher your pH is going to rise, and the faster it's going to rise. Because like champagne versus a beer, if you have more carbonation to begin with, meaning more alkalinity in this analogy, it's going to have a more violent off-gassing. And this of course can be accelerated with people splashing around, sprayers, spa jets, spillways, all that sort of stuff.
[00:15:54] So, uh, is there anything else on liquid chlorine that I'm missing before we move on to cal hypo?
[00:15:59] Terry Arko: I think we're there.
Cal Hypo (calcium hypochlorite)
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[00:16:00] Eric Knight: Okay, so now instead of sodium hypochlorite, we're going to move to calcium hypochlorite. Uh, cal hypo, as we did in a previous episode. It comes in various strengths. The two, like trade grade, or professional grade, products are usually labeled either 65 or 68%, or 70 or 73%.
[00:16:22] One of them is the weight percent, one of them is the available chlorine percent. You also have some cal hypo shocks that I've seen at Home Depot and Walmart that are lower percentages. God knows what else is in there. Maybe there's some filler products, who knows? But I have seen stuff that's like 56% and 42%, and who knows?
[00:16:41] So when you're trying to figure out how much you need, it's really important to understand those percentages. But regardless of that, guess what they are also relatively pH neutral. And the reason for that is the exact same reason that we just went through with liquid chlorine.
[00:16:57] So, Terry, you want to elaborate?
[00:16:59] Terry Arko: Yeah. So with the sodium hypochlorite, you're producing the HOCl along with sodium hydroxide, which is that immediate increase of the pH. But with calcium hypochlorite, same thing. Cal hypo comes in contact with water and you are going to immediately create HOCl. And the byproduct of that is going to be calcium hydroxide.
[00:17:25] Eric Knight: Now, hold on Terry. Calcium hydroxide is the same substance, you've probably heard this before when we talk about plaster, it's the same substance when you hydrate Portland Cement. Calcium oxide, CaO, blends with water to create calcium hydroxide. It's about 24 to 27%, so we'll call it a quarter of your cement matrix.
[00:17:46] That's the stuff that causes the plaster issues. That's what water dissolves because it's more soluble. That's what gets pulled to the surface and carbonates into pure white calcium carbonate, which we call uneven carbonation. It's the stuff that becomes plaster dust when it's carbonated. It is the most common thing that gets affected in swimming pools that have cement finishes. Calcium hydroxide, and yet cal hypo's byproduct is the exact same substance.
[00:18:12] Terry Arko: Yes.
[00:18:12] Eric Knight: 12.6 pH, right?
[00:18:14] Terry Arko: Yep. And so obviously immediate pH raise is going to occur from the reaction of cal hypo immediately with H2O.
[00:18:24] Eric Knight: Right. it says here in Lowry's book on page 134, and I'm quoting, Calcium hypochlorite adds alkalinity to the pool water, but does NOT ( all caps) increase the pH. It has a pH of 10 to 11.8, and initially it will raise the pH. However, when the HOCl is used in killing or when degraded by sunlight, that HOCl is converted to HCl, hydrochloric acid. The amount of acid produced is almost the same amount as the hydroxide produced when added. So the net pH result is almost zero.
[00:18:56] Sound familiar? That's exactly what we just said about liquid chlorine. So it's the exact same thing.
[00:19:01] Terry Arko: It is the exact same thing. In Southern Cal we didn't deal much with Cal hypo, but obviously, later on in my career teaching chemistry, traveling around the country, same thing. Talking to a lot of pool service techs and they're on Cal hypo and they're automatically using a certain amount of acid with the cal hypo to keep the pH down.
[00:19:22] Eric Knight: I can understand that and let's talk about that for a second before moving on to the stabilized chlorines. Every single time I've used cal hypo, granular, I should say, it clouds up.
[00:19:32] Terry Arko: Mm-Hmm.
[00:19:33] Eric Knight: Can you explain why that cloud's up? And what our listeners can do to prevent it from clouding up?
[00:19:38] Terry Arko: Yeah. If you're adding that straight into the pool. When that's hitting the water, you're getting an immediate raise in the pH. And when you do that, any calcium that's in the water is going to precipitate out as calcium carbonate.
[00:19:52] Eric Knight: As we mentioned just a minute ago, liquid chlorine will also cloud up the water if the pH is already pretty high. If it's not that high, I mean, I did it in my backyard at 8.02 pH ceiling, and it never clouded for me because it doesn't contain calcium, specifically calcium hydroxide.
[00:20:08] So not only are you forcing an LSI violation because the temporary spike in pH, which converts bicarbonate ions into carbonate ions, which then look for calcium in the water, which by the way, you just added. You're also increasing the calcium hydroxide, which has a 12.6 pH and, and, and, and.
[00:20:27] So it's kind of like this perfect storm of all these things that are going to create cloudy water in the very short term. Now, it will disperse because as the concentration goes down, the LSI can kind of resume. So how can people prevent that? What can you do to the water to use cal hypo effectively if you're shocking with a granular product?
[00:20:47] Terry Arko: Well, I mean, again, it gets into balance and it gets into the LSI, and where you're keeping your LSI. And again, not having a high alkalinity, and also managing your calcium levels as well.
[00:20:57] Those are the two things that I see when somebody's got a very high calcium hardness along with high alkalinity as well. Just the two of those alone, if they get high enough, um, you've got the potential of calcium carbonate just from that. But then when you spike the pH, then you really are going to precipitate calcium carbonate.
[00:21:14] Eric Knight: Should, should we follow the same procedure that we just talked about with liquid chlorine of adding diluted acid to take the edge off a, you know, a couple minutes before you add pre dissolved cal hypo?
[00:21:27] Terry Arko: Very good idea. Yeah. And that's, that's how I would do it.
Sodium Dichlor (dichloro-s-triazinetrione)
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[00:21:30] Eric Knight: Okay. let's keep moving. Now we're going to get into the stabilized chlorines. Uh, we'll start with sodium Dichlor Dihydrate. Dichlor in this product, it has a pH when it dissolves of between 6.5 and 7.0, so that's pretty neutral.
Trichlor (trichloro-s-triazinetrione)
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[00:21:46] Eric Knight: Trichlor is far more acidic. According to this, it has a pH between 2.8 and 3.0. that's a figure that we've all heard before, I think, and we're talking about three inch tabs. If you're not familiar with trichlor, when you look at it on the label, it'll say trichloro-s-triazinetrione, that's basically what we're dealing with here. Very, very common product. And because it's acidic. It is going to actually impact your pH of your pool.
[00:22:15] So Terry, you were witnessing back in the seventies and eighties when you were cleaning pools. You were leaving tabs in the pool all week long and you'd come back and the pH never really climbed that much because you had trichlor long-term.
[00:22:25] Terry Arko: Mm-Hmm.
[00:22:26] Eric Knight: Explain what was really going on.
[00:22:28] Terry Arko: Well, the trichlor that was being used there was lowering the pH, uh, but also lowering the alkalinity too. Because that's what trichlor would do. Alkalinity is constantly going down. That's pulling the pH down. So,
[00:22:40] Eric Knight: Let's expand on that because that ties into the carbonate alkalinity equilibrium once again. Because we have alkalinity in our water. If we want to lower the pH, we have to produce more CO2. Dissolved CO2 is called carbonic acid. This is carbonic acid and bicarbonate in equilibrium.
[00:22:56] By the way, if you have the Orenda app, open up the calculator and show secondary readings at the top left and tap on the hyperlink that says carbonate alkalinity. And you'll see a chart. That's the chart I'm referring to. The red line is carbonic acid, H2CO3.
[00:23:13] What trichlor and other acids do is they add a hydrogen, which is the acid, to a bicarbonate ion, which is HCO3-, and it becomes H2CO3, which is dissolved CO2, carbonic acid. H2O plus CO2 creates H2CO3.
[00:23:32] And what it's doing is it's converting, or as I say, and this is obviously in layman's term, Terry, acids sort of burn through alkalinity to create more dissolved CO2
[00:23:43] Terry Arko: right.
[00:23:43] Eric Knight: and that's what lowers the pH.
[00:23:44] Terry Arko: That's exactly right.
[00:23:46] Eric Knight: yeah, you're harvesting alkalinity, you're burning through it, and the smoke is CO2. Which gets into your water temporarily, but then you've just recarbonated your water. You've recarbonated your beer, and that beer now has to go flat again. So you're going to lose that, pH is going to come back up.
[00:24:02] But Terry, because it's acidic and it's slow dissolving, this is a constant drip. It is keeping the pH down. It is suppressing the pH. Not controlling it, but it's suppressing it.
[00:24:13] That being said, how should trichlor actually be used, and where should it never be used in a swimming pool?
[00:24:20] Terry Arko: The inappropriate place would be never in the skimmer.
[00:24:23] Eric Knight: Where's the right place to put it?
[00:24:25] Terry Arko: An inline chlorinator that's specifically for trichlor located in a place where it's going to be downstream of any or all equipment, like your pumps and your filters and your heaters. because Again, it's, it's acidic and if it's anywhere near any sort of heat exchangers, copper, those kinds of things, you can have problems.
[00:24:45] And the reason I said never in a skimmer is again, your skimmers in front of everything. And the thing about trichlor tablets is they are erosion tablets. They're designed to erode whether water's running over them or not. And so if they're sitting in the skimmer, even if the pump's not running, those tablets are wearing down. And whatever water is in that skimmer, whatever amount, a few gallons, I don't know what it is, but it is going down to a pH towards, you know, maybe three.
[00:25:14] Then you turn the pump on, the first water that's going to be going through your system is very acidic water, which is corrosive, and it's going to damage any copper that's in that system anywhere, um, and strip things out. So you, you never want to do that.
[00:25:29] Eric Knight: I just want to reiterate what Terry is saying is absolutely correct. We see a lot of problems with people that put trichlor tabs in a skimmer. I understand it's easy, and this goes for you homeowners out there too. Avoid the temptation. I know it's easy to drop a puck in the skimmer. Please don't do that unless you want to buy all new pool equipment, in which case that's on you.
[00:25:48] But don't do it. It will wear down. And one thing that we see a lot of, I believe it or not, I see a lot in like outdoor spas. And when I'm in California, a lot of green spas, and that's because the trichlor is destroying the heat exchanger, oxidizing the copper, and it's putting it on the surface.
[00:26:05] Terry Arko: Yeah, absolutely. I took over one when I serviced pools in Southern California. And I took on a new one, and it was a condominium that had an in-ground white plaster 10 foot round spa that the person who previously was taking care of it was using trichlor tablets in the skimmer. So that white plaster, 10 foot round spa was now emerald green. And everybody at this condominium that had been there, it had been that way so long, they actually thought that the color of the plaster was emerald green.
Saltwater Chlorine Generators (SWG)
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[00:26:36] Eric Knight: It's not, at least it's not supposed to be. Okay. Let's move on to salt chlorine generators. Now, as we know, a salt pool is a chlorine pool. If you didn't already know that, welcome to the podcast. This is called Rule Your Pool. We're glad to have you.
[00:26:51] Uh, Terry, there is a obvious phenomenon that goes on in a salt water pool, and that is that the pH rises. There's no doubt about that. And it's funny that before I get into this, I was just at a show watching a salt presentation. And they were explaining that it creates liquid chlorine. That is not what a salt system does. Now, the net effect of it is very similar to liquid chlorine, but it is not creating liquid chlorine. It has to do with how it dissolves in water.
[00:27:22] So here's exactly what salt system actually does. You got salted water going through an electrical situation that's called, electrolysis, I think.
[00:27:33] Okay. That electrolysis converts in the sodium and the chloride from salt split, and it converts that chloride into chlorine gas. And then because the sodium is dissolved in the water, the other byproducts are sodium hydroxide and hydrogen gas. Now, hydrogen gas is not the same as hydrogen ion, which is a pure acid. But chlorine gas, as we'll explain in a moment, is a pure acid when it dissolves in water.
[00:27:59] So you got this pure base sodium hydroxide, and you have this pure acid, chlorine gas. And then you have this hydrogen gas H2, and that's what the bubbles are.
[00:28:10] So the bubbles that you see, if you've ever been cleaning a salt system in a bucket or something like that, and you turn it on and there's bubbles, A, don't breathe them, but B, some of that's hydrogen, some of that is chlorine gas. And the turbulence that gets created by those bubbles actually releases carbon dioxide from the water.
[00:28:29] So it's like at a molecular level, you're creating a lot of turbulence. And I understand like assault system's, what, a foot long maybe? Depending on the system you have. And water's moving 50 to 60 gallons a minute sometimes. So it's not even in there for a split second. But that's plenty of time at this molecular level for this chemistry to happen.
[00:28:48] Here's the misconception. People assume because it creates sodium hydroxide, caustic soda, which is the base, that the salt cell chemically raises the pH of the pool. And as Terry's going to explain to you, that's not what's actually happening because six feet down the line that pure gas called chlorine and that pure base neutralize each other, and it's actually the most neutral form of chlorine you can have.
[00:29:12] What raises the pH is physics. It's the loss of CO2. Alright. How'd I do Terry?
[00:29:18] Terry Arko: you did great. The basic thing here is that you've got the sodium chloride going through electrolysis where you have two differing cells. One has a positive charge, one has a negative charge.
[00:29:29]
[00:29:31] Terry Arko: Anode and the cathode. Okay? So that positive sodium is drawn to the negative, and the negative chloride gets drawn to the positive end. So at that positive end, you're creating chlorine gas. and at the other end you're creating the sodium hydroxide and the hydrogen gas.
[00:29:49] And that hydrogen gas creates those bubbles. Those bubbles create turbulence, and that's aeration. And when you aerate water, CO2 leaves the water and the pH increases. The other thing is that. There's a thermodynamic reaction going on in that small amount, like you said, that small amount, uh, of distance, uh, so all those reactions going on in there and the electrolysis, you're heating the water as well. The water in that area is very warm. And we know from LSI, if the temperature goes up, what else goes up?
[00:30:22] Eric Knight: The LSI does.
[00:30:23] Terry Arko: The LSI and The pH along with it. So you've got two things going on in there. And as you said, it's not chemical. You are producing pure chlorine gas and sodium hydroxide. And so once you get downstream, that's neutralizing . So, it is from the aeration in that unit that cause the pH to increase.
Chlorine Gas (Cl2)
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[00:30:43] Eric Knight: So we're going to talk about chlorine gas because salt systems create that chlorine gas, and as we just said, it's a pure acid. When we talk about pH potential or power of hydrogen, the acid is the hydrogen ion. There is no hydrogen ion in chlorine gas. It's just a Cl2. So tell us what happens when you dissolve chlorine gas in water?
[00:31:05] Terry Arko: When I talk a lot about the science of water in the beginning of my chemistry classes, you know, there there's a process called hydrolysis. So what does that mean? It means that water through hydrolysis has the ability to break down any compound it comes in contact with, or molecule or anything.
[00:31:22] So Cl2, you're right, there's no hydrogen there. But as Cl2 goes into water, hydrolysis kicks in immediately, and you're going to create the HOCl. And that's just going to get pulled from the water molecule itself, because what is water? Water is H2O.
[00:31:39] It's got two positive hydrogens and a big negative oxygen on it. Hydrolysis kicks in and you start splitting off some of those hydrogen ears. And then that attaches to the Cl2 and then the oxygen is there as well. That's where you're going to create that pure hypochlorous acid from the Cl2.
[00:31:59] Eric Knight: So I've got the equation in front of me. When you dissolve Cl2 in water, Cl2 plus H2O yields HOCl, which you just said, it also yields hydrochloric acid. So not only are you creating hydrochloric acid, which is the actual substance that we call muriatic acid.
[00:32:15] Although I think Terry, as an aside, muriatic acid is a lower percentage of hydrochloric acid. It's 31.45% or less. Is that correct?
[00:32:26] Terry Arko: Yes. And that's just due to, um, it's blended with more water.
[00:32:30] Eric Knight: It is safer to handle. Okay, so muriatic is hydrochloric. It's just a lower concentration.
[00:32:34] Terry Arko: Right. I mean, hydrochloric acid is basically hydrogen chloride dissolved in water. The percentage of it has to do with the amount of water they dissolve it in.
[00:32:43] Eric Knight: Okay, got it. So it's creating hydrochloric acid, but then the HOCl as we know is going to do its job and it's going to create more hydrochloric acid. So that is why chlorine gas is a pure acid.
[00:32:58] Like I said, in a salt system, that chlorine gas neutralizes the sodium hydroxide down the line. Salt systems are pH neutral. I know it doesn't sound right, but it is. Because it's not the chemistry that raises the pH in a salt pool. It's the physics. Big difference.
Closing
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[00:33:16] Eric Knight: I think this answers a lot of the questions that we get. If you have more questions about chemistry, feel free to email me, podcast@orendatech.com. You can also go to our help center, which is ask.orendatech.com, and then you can submit a question at the top. I know a lot of you people are doing that. These are just phenomenal questions we get. And it really helps us because it tells us what we need to be writing.
[00:33:38] If you have questions that are not already on our website or we have not yet discussed on the podcast, you're helping us by asking us those questions. So don't feel like you're pestering us by any means. Please ask the questions. They really help us get better and they, in turn, help us teach the entire industry. Because if you're asking that question, I can promise you you're not the only person asking it, or at least wondering about it.
[00:34:00] Terry, anything else you want to say before we go?
[00:34:02] Terry Arko: No, this has been awesome. Very glad to be a part of this, Eric.
[00:34:06] Eric Knight: Cool. Happy to have you here. And I do just want to add, uh. If you are watching on video, at least we'll see how this renders out. But your video quality is absolute garbage. And I just want to laugh about it because, uh, you know, people say, people say there's no difference between Microsoft and Apple,
[00:34:22] Terry Arko: Yeah microsoft's given me like a, a peaked head there. I've got a,
[00:34:27] Eric Knight: Yeah, it's like looking, it's blurring out your background. This is hilarious. And at one point you had, it looked like you had something on your head, but.
[00:34:34] Terry Arko: Like it's very possible. Who knows?
[00:34:37] Eric Knight: Yeah, j Just for those of you who are listening, uh, Terry has this like blurred out background kind of template thing and he can't get rid of
[00:34:43] Terry Arko: Yeah.
[00:34:43] Eric Knight: he doesn't know how to get rid of it. So here we are. Yeah. We're doing what we can when we can. So anyways, this has been episode 135 of the Rule Your Pool podcast. I'm not sure what we're going to talk about next time, but Terry will probably be on that next episode or the one after that. We have a lot of questions that have come in.
[00:35:00] We have a lot to cover. And we are almost done with trade show season. We're about halfway through, so we're in the home stretch. Everybody, thank you so much for listening and uh, we will see you next time. Take care.
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