Myth vs. Reality: Pool Chemicals Edition

Tired of pool rules that don’t add up? We peel back the layers on the industry’s most persistent myths and replace them with chemistry you can trust. From the “acid column” idea to the belief that liquid chlorine always drives pH sky high, we show where the logic sounds right and why the science says otherwise. You’ll learn how acid truly mixes on contact, why slugging can scar plaster and vinyl, and how to dose safely using circulation to your advantage.

We also tackle the big one: “chlorine lock.” Chlorine isn’t trapped; it’s either free, combined, or used. The real driver of effectiveness is the free chlorine to cyanuric acid ratio. Using the 7.5% guideline, you can set targets that outpace algae, save on unnecessary algaecides and shock, and keep water clearer with fewer surprises. We talk testing too—why relying on old OTO “flash” habits keeps you in the dark, and how FAS-DPD reveals what’s actually happening so you can correct fast.

Finally, we clear up confusion around safe swim timing. That 24-hour wait after adding chlorine? Not a rule of nature. It’s about how much you dosed, how well the water circulates, and where your CYA sits. Light dosing with proper CYA can be safe much sooner, while heavy shock may warrant patience. With muriatic acid, circulation and pH verification matter more than the smell—often making a 30–60 minute window reasonable for re-entry in large, balanced pools. Walk away with practical steps that protect surfaces, stabilize pH, and restore confidence in every service visit.

• acid column method risks surface damage and does not target alkalinity
• liquid chlorine raises pH briefly, then neutralizes as it oxidizes
• cal hypo truly raises pH, liquid chlorine trends near neutral net effect
• chlorine states: free, combined, and used chloride
• no such thing as chlorine lock, just high CYA slowing chlorine
• maintain free chlorine at ~7.5% of CYA for effectiveness
• accurate testing beats OTO flash tests for FC and CC
• safe swim timing depends on FC-to-CYA and circulation, not 24-hour rules
•

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Chapters

• 0:00 Welcome And Coaching Invite
• 2:33 The Acid Column Myth
• 5:43 Why Acid Mixes Instantly
• 9:21 Liquid Chlorine And Temporary pH Rise
• 14:29 “Chlorine Lock” Explained And Debunked

Transcript

SPEAKER_00: 1:03

Hey, welcome to the Pool Guy Podcast Show. In this episode, I'm going to go over some common myths and misconceptions about chemicals. Some things have been believed industry-wide, and I'm going to try to at least debunk these a little bit here and kind of bring some clarity and truth to these kind of myths that have been propagated in the industry over the years. Are you a pool service pro looking to take your business to the next level? Join the Pool Guy Coaching Program. Get expert advice, business tips, exclusive content, and get direct support. From me, I'm a 35-year veteran in the industry. Whether you're starting out or scaling up, I've got the tools to help you succeed. Learn more at swimmingpoollearning.com. If this one's been around ever since I got into the industry, it's called the acid column or the slug method. And this is a myth where it depends on how you add the acid to the pool, how it will affect the pH and alkalinity. For example, the acid column or slug myth says that if you stand in a deep end and pour all the acid into the water in one place, this lowers the alkalinity versus walking around the pool and pouring the acid in slowly around the perimeter, and this will lower the pH. And I'm unsure of how this myth got started. It does make some sense if you think about it. If you were to think of like shocking the pool with acid, I guess would be the concept, and that would lower the alkalinity rapidly. But in reality, the acid does the same thing, it lowers the pH and total alkalinity at the same time. In fact, the column method is actually not good for the pool surface, especially if you're pouring it in a vinyl pool or fiberglass pool, or if you're standing in shallow water, pouring half a gallon of acid into the pool in one location is not the healthiest thing. Even though you have, you know, 10,000 gallons of water in there, you really don't want to do that, and you could cause actually damage to the pool. So the theory behind this is that if you pour all the acid in one column, it attacks the alkalinity at the bottom of the pool, and it total total alkalinity drops without lowering the pH much. So there is a kind of visual logic behind this. You'll kind of imagine the acid settling to the bottom of the pool. And the problem why this doesn't work is that muronic acid is actually heavier than water, and it diffuses immediately. It doesn't kind of just clump there, like if you were to pour syrup or maybe an agave into a tea, and it's just not going to be at the bottom of the cup like you would think. And it's something where the acid and water mix together very rapidly at a molecular level. So it really doesn't matter how you pour it in. It just is one of those things where it doesn't work. It's just one of those myths that have been propagated that on the surface, pun intended, appears to work because you're pouring all the acid into the pool, but there are also realistic factors working against it. For instance, toloccalinity is evenly distributed in the pool, so attacking one area of the pool is not going to lower it because it's not all concentrated on the bottom of the pool. And it's one of those things where you're actually risking damaging the plaster or pool surface by doing this. This next one isn't technically a myth, but it's been believed in the industry for a long time. It is something that doesn't really you can't really break through this one without really unpacking chemistry at a molecular level. And this is why this one kind of sticks around, and even if you explain the chemistry, people still don't believe it because you look at the chemical and you know that it has a higher pH than the water itself. And logically, when you're adding a chemical at a higher pH, the pH rises in the pool. And I'll phrase this one liquid chlorine raises the pH in the pool temporarily. And that's the truth behind liquid chlorine, even though it has a high pH of 12 or 13, and if you're adding one or two gallons, of course, logically the pH is rising in the pool because it's a high pH product. However, it does raise the pH in the pool temporarily. So the chemical reaction, and I'll try to keep it as simple as possible, when sodium hypochlorite, which is the chemical that makes up liquid chlorine, hits the water, a chemical reaction occurs where hydroxide is produced. So hydroxide will raise the pH. So right after dosing, the pH goes up. But when the chlorine is active and oxidizes and kills algae and other elements in the pool, it actually forms an acid which lowers the pH. And you can look up the chemical reaction, I'm not going to explain it here, but basically, when you add it to the pool, it creates a higher pH reaction through the chemistry of the chlorine. And then when the chlorine actually starts to activate oxidizing the water, it creates an acid that lowers the pH, or it affect cancels itself out. It doesn't technically lower the pH in the pool, but it will lower the high pH that it created when you first put the liquid chlorine in the pool. This is why it's so hard to get rid of this particular teaching in the industry where everyone has been taught that liquid chlorine raises the pH. We know that cow hypo raises the pH, but as far as liquid chlorine raising the pH, yes, it does raise it. Initially, when you pour it in, it raises the pH, but then as it's active, it actually produces an acid that makes the pH or it neutralizes what it raises. It's kind of like shaking a soda can. When you shake it, it's kinda kind of like adding chlorine. You're building pressure, so the pH rises. So again, like a soda can when you shake it, it's like adding chlorine, and then the pressure builds, which is the pH rising. When you open it, and of course stand back when you open it, chlorine gets used up, the gas escapes, and it settles back down. So again, it's a temporary rise based on the chemical reaction, and then it settles back down. It's actually a pretty simple concept if you think about it long enough, and it's something that of course has been in the industry for ever a very long time that that liquid chlorine raises the pH in the pool. Here's one that's been around ever since I started as well, and this is the term chlorine lock. The chlorine is locked up and not effective. Now, there is a little bit of truth behind this, but the chlorine is never actually locked up. Chlorine is in one of four states, and it's really simple as this. You have the free chlorine, which is active, plus the reserve. Then you have the combined chlorine, and if you have pools with this, you've smelled it before, like an ammonia smell. The water is typically cloudy. Then you have chloride, which is the used upstate of chlorine, and so there's never a state where the chloride is actually locked up. Now, what what is part of this is that the high cyaneric acid in the pool makes the chlorine less effective and it feels like it's locked up, but it's really not locked up. So there's either not enough active chlorine in the pool, it's bound to the cyaneric acid and equilibrium, it's already consumed, or it's not being tested correctly, and a lot of times it's not being tested correctly, because back in the old days, a lot of us did flash testing with the OTO, and that's not an accurate way of testing it for sure. I still see guys actually doing the flash testing. They have like a little pouch they wear, and they have the OTO and the and the phenol red in there, and they're just dropping it in there and trying to get an accurate reading that way, is not possible. So this myth has been propagated because it does sound technical and it does almost have some accuracy to it, but not quite, because there's a lot of factors that cause the chlorine to be ineffective in the pool. And it really sometimes just by saying the chlorine is locked, you don't have to worry about explaining the free chlorine to cyanuric acid ratio in the pool. And it's a convenient way to sell algecides and more shock to somebody that comes into a pool store, for instance, or you know, even a lot of pool techs will buy into this that the chlorine is locked up in the pool, and they they spend a lot of money trying to quote unquote unlock it by shocking the pool, adding algecides. But it's really a simple thing, and the key is to understand the free chlorine to cyaneric acid ratio. And if you heard me, I talk about this all the time. It's Bob Lowry's formula is 7.5% of free chlorine to cyaneric acid. So if your cyaneric acid is 100 parts per million, for the chlorine to be effective and not to be, quote, locked up, it needs to be at 7.5 parts per million or 8 parts per million to be make it easier for it to be effective in the pool with the cyaneric acid level at 100 parts per million, because the cyaneric acid does slow down the chlorine's ability to work in the pool, kill bacteria, and fight off algae in the pool, but it's certainly not locked up in any sense of the word or the term as it's been kind of put out in the industry. The chlorine is not locked up and not effective. There's there's many reasons, not many, there's a few reasons why the chlorine is not effective. You may not have enough chlorine in the pool. So if you're at 100 parts per million of cyanuric acid and you have five parts per million of free chlorine in the pool, you don't have enough chlorine for it to be effective in the pool because the cyanaric acid level is higher than the percentage ratio you need to reach with the free chlorine. You could have combined chlorine in the water, making the chlorine ineffective as well. So there are some reasons behind why the chlorine is not effective and it's not locked up in any sense of that term. And this myth probably originated because you can actually see this happening in some pools where if you have a higher cyaneric acid level than the free chlorine level, you'll see the algae accelerate and spread through the pool, and that's because the algae is the algae is spreading and growing faster than the chlorine can kill the algae, and this kind of gives you this, you know, okay, the chlorine is locked up and the algae is spreading, and therefore this is where kind of this came from. I think this is you know when you look at a pool where the algae is spreading and the chlorine can't keep up with it, you would think that the chlorine is locked up in some way, but there's just is not enough free chlorine and it's not killing and working effectively or as faster than the algae growth in the pool. So this concept does make sense, but in reality the chlorine is never again locked up. Here's another one that you hear often, and it comes in different forms and time lengths, and you hear this one a lot. You can't swim in the pool for 24 hours after adding chlorine. I've heard other ones, you know, six hours or five hours, and this one here really is interesting because the reality behind it is that if you just added it about 10 minutes ago, you know, with the with the proper CYA level in the pool, it's actually safe to swim in the pool. And a lot of this came from commercial pool rules that says, of course, you have to if you've done commercial pools before and get there later than early morning, the pool's already being used, and so what you need to do is have everyone get out of the water, and you know the rule requires not adding chemicals while bathers are in the water. That makes perfect sense to me. You don't want to be adding chlorine and myratic acids to the pool where there's people in the water itself, and there's a wait time after, because there's some liability, of course, for the bathers in there if you're adding chemicals while they're in there. And the you know, the old school shock instructions also taught that you would shock at you know in the evening or at night time and you wouldn't swim until the next day late in the afternoon. Because when you shock the pool, of course the chlorine level gets gets extremely high in the pool, bringing it to 10 parts per million or higher. And it's something that you we've have ingrained in us that if you bring the chlorine level up to a certain point, it's not safe to go in the pool. But if you just listen carefully to the last segment and you had cyanaric acid at 100 parts per million, you would need 8 parts per million of free chlorine for it to be effective. So if you had your cyaneric acid level at say 200 parts per million, which is not unheard of in Southern California with the use of trichlor tablets, you would be safe to swim in that pool at 14 parts per million. So it's not a matter of how much chlorine you add to the pool, it's a matter of the cyaneric acid level as well, with that formula of 7.5%. I know it's confusing, but you could safely swim in a pool with high chlorine if the cyanaric acid is really out of range and really high in the pool as well. So if the cyanaric acid level is at 50 parts per million, you can safely swim in the pool, even if the cyan even if the free chlorine is at you know eight parts per million, that's perfectly acceptable. And if the free chlorine is at 20 parts per million, of course, if you just shocked it, you want to wait till it drops down to close to 10 parts per million before you get in the pool. So the 24-hour rule is not something that's cut and dry, and it's not something that if you add you know half a gallon of liquid chlorine, you have to wait, you know, 24 hours. You may not, depending on the cyanaric acid level and how much that brought the chlorine level up to. And it's no there's no hard and fast rule, I should say, of when you can go back into the water. Sometimes you can get back in there 10 minutes after, sometimes you should wait an hour or two. Sometimes if you shock the pool and bring it to 20 parts a million, waiting that 24-hour period may be logical. So again, you really can't say by adding a certain amount of chlorine, you have to wait a certain amount of time, 24 hours, six hours. It's all a matter of math, and it's a matter of knowing that the higher the cyanuric acid level is, the higher tolerance for free chlorine there can be in the pool. And it's not something, again, you know, if you pour chemicals in, you have to wait 24 hours. Now, as far as muratic acid goes, it sounds like this is also something that you should wait a very long time to get into the pool after using, especially you know, the 31% muratic acid, and you can smell the chemical when you're pouring it in, and it is it's actually really strong. But in reality, if the pool is actually running and circulating, and you're adding, let's say, you know, you have a 20,000 gallon pool and you're adding a quart of muratic acid to it to get the pH from 8 to 7.8, it's really at a level already in the pool where it's not going to bother the bather, it's not like at 7 where they're going to start getting itchy skin and burning eyes. And if the pool is running and circulating, you can actually get in the pool probably within 30 minutes to an hour after adding it, as long as the pH has gotten to a certain level. It's not like the acid stays in one area of the pool and is concentrated in that area. So you can actually swim safely in a pool after adding maric acid a lot sooner than when you add chlorine to the pool, because if the pool is circulating, the acid is dissipating. As long as the pH is not dropping to a level where it irritates the bather, there's really no danger to it because think about how much water is in the pool compared to how much acid you just added to the pool. And again, the pH is the key, the level of pH is the key versus the perceived strength and potency of the maritic acid. And if you're looking for other podcasts, you can find those on my website, swimmingprolearning.com. On the banner, click on the podcast icon. There'll be a drop down menu of other podcasts for you there. And if you're interested in the coaching program, you can learn more at PoolGuyCoaching.com. Thanks for listening to this podcast. Have a good rest of your week. God bless.