Why “Shocking” Your Pool Isn’t a One-Time Fix

“Shock the pool” is one of the most overused phrases in pool care, and it causes a lot of bad advice. We walk through what shocking really is: raising free chlorine to a level that actually matches the pool’s chlorine demand, then giving it time to work and verifying it with testing instead of wishful thinking. If you’ve ever added gallons of chlorine and still seen the test read zero, we explain why that happens and how to avoid the endless loop of underdosing and retreating. 
 
We share real, field-friendly targets for green pool cleanup and mustard algae, including a simple ballpark ratio for severe cases and why many pros would rather push chlorine to 40 to 50 ppm than gamble on a “perfect” calculator number. We also cover swimmer safety, what level you need to drop to before the pool is safe again, and why the pool can look dramatically better while the chlorine reading crashes overnight. 
 
Then we clear up confusion around non chlorine shock (potassium monopersulfate): where it shines for pool parties, oils, and chloramine odor, and why it will not fix algae. Finally, we dig into the factor that quietly wrecks many shock attempts: high cyanuric acid (CYA), how it changes chlorine effectiveness, and why generic bag instructions can’t account for your water. 

• why low chlorine leads to green water and algae blooms
• shocking as a process of reaching and holding a chlorine level
• a ballpark dosing rule for severe green pools and mustard algae
• why a zero reading can behave like “negative chlorine”
• when aiming for 40 to 50 ppm prevents underdosing
• swim safety and waiting until chlorine drops below 10 ppm
• what non chlorine shock is and when it actually helps
• why high cyanuric acid changes effective chlorine needs
• what to expect on day two after a heavy shock
• using phosphate remover, enzymes, PoolRx, and algaecide to speed cleanup

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Transcript

Why Pools Turn Green

A Simple Chlorine Dosing Ratio

When Zero Chlorine Is Not Zero

Targeting 40 To 50 PPM Safely

Non Chlorine Shock Explained

Why CYA Changes Everything

What To Expect The Next Day

Enhancers Like Phosphate Remover

Where To Find More Resources

SPEAKER_00 1:02

Hey, welcome to the Pool Guy Podcast Show. In this episode, I'm going to talk to you about shocking your pool. And of course, the first thing that you have to know is that shocking is not actually something that is a one-and-done thing. It's actually a process. And I'm going to go over the process with you and kind of fill in the gaps when you say shocking a pool. 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 swimming poollearning.com. One reason why a pool may turn green or have algae is because it has too little chlorine in it. And this is one of those things where it's just something that you have to understand that when you say shock a pool or you go to the pool store and they say you need to shock the pool. That's kind of a one-word that explains the whole actual process of it. And it's kind of become an industry standard for some reason. We just say shock the pool or add shock to the pool. And you're supposed to know exactly what we mean by that. And the person behind the counter at the pool store says that. The customer is expected to know exactly what is meant by that. It's like if someone says bake a cake, that means go bake a cake. But of course, there's things involved in that. You gotta, of course, break some eggs and get the cake mix and all that stuff. I don't know how to make a cake, but basically, you need to get all the ingredients together, put it in the oven for a certain amount of time and temperature, and then you bake the cake. Same thing with shocking a pool. It's just a term used for the process. And this means adding chlorine to a certain point. Yes, you're adding chlorine to the pool to a certain point. And what point is that? Now here is where it gets really confusing. And it's kind of like when you're baking a cake and you get a toothpick and you stick it in there to see if it's done or not. And if it comes out kind of gooey, then you know it's not finished. Well, when you're shocking a pool, you can't do that because if you dip the toothpick, let's say, in the pool, which is your test strip, you pull it out and it's showing zero chlorine, you have a problem because you've shocked the pool, you've added 10 gallons of liquid chlorine or whatever. The next time you test it, you're at zero. It's a big problem because you didn't add enough chlorine to the pool to do what you need to do to that pool, depending on if it's cloudy, green, yellow algae. Because a lot of things happen when you add the chlorine to the pool, and you don't really get instant results. Again, it's like putting a cake in the oven. You have the oven set at 400, put the cake in there, and after one minute, the cake is not solidified, it's still gooey because it takes time for that to bake. The same thing when you add shock to a pool, it takes time for that pool to kind of bake, get to the right chlorine level to kill the algae in the pool. For example, if the pool is really green, there's mosquito larvae forming in the pool, and let's just say it's a 15,000 gallon pool, and you put it in two gallons of liquid chlorine. Nothing's gonna happen because it's just like putting basically pouring water into the pool at that point because there's so much algae in the pool that that two gallons of liquid chlorine are gonna do nothing to the water. Now, if the pool is that bad and it's 15,000 gallons, you're gonna need to add probably. I have a ratio of chlorine per gallon of water, and this seems to be a pretty good ballpark ratio to use when you're trying to get a pool from green black to kind of murky blue, it's not gonna be blue right away. Is every for every 1,000 gallons of water, you're gonna add one gallon of 12.5% liquid chlorine or one pound of cal hypo to the pool. And this equation has served me pretty well over the years. I I kind of did this unconsciously. I'm kind of the person that overdoes it, then underdoes it, and I've always been paranoid about putting too little chlorine in the pool, so I'm always overdoing it. I'm kind of heavy-handed, I'll admit it when I'm shocking a pool. Now, this formula is only for a green pool or a pool that's like completely covered in mustard algae. This formula is not for a pool that's kind of blue, murky blue. You can see at the bottom, but it's cloudy. If this ran out of chlorine, there's really not a lot of algae in the pool. Then you would want to do a 20 parts per million, bring the chlorine level to 20 parts per million or 30 parts per million. That may sound like a lot of chlorine, but it's really not. So if the chloride is at zero and you have a 15,000 gallon pool, you would add about three gallons of liquid chlorine at 12.5% strength to bring it up to the 20 parts per million. Let me get you the cal hypo number here so you can see how much cal hypo you need to add for the same exact uh pool if you're gonna use cal hypo. You'll need about four and a half pounds of cal hypo, 73% cal hypo, to bring it from zero to twenty parts per million. But there is a problem with even using a calculator to get the 20 parts per million number, and that is the fact that the chlorine is at zero, but it could be actually negative chlorine. The way I describe this is that there are factors in the water that make that zero more like a negative 10. You know, algae in the pool, black algae, yellow algae, the pool is really cloudy. The pool smells like ammonia, there's like a lot of chloramines in the water, and you have this really strong Windex smell. There's probably a negative coin level, even though there's no such register of a negative coin level when you do the test, it just shows zero. So if you're at negative 10 and you're gonna bring it to 20 parts per million, you're actually bringing it to 10 parts per million. So you're gonna actually have to bring it to 30 parts per million. There's a process in trouble-free pools where they actually bring it to like 50 parts per million, and I think that's a fair way to make sure that you have enough chlorine in the pool and you're not gonna have any kind of errors with adding too little chlorine. So instead of shooting for you know the breakpoint chlorine level, you know, the breakpoint if it has chloramines, go ahead and just go for 40 or 50 parts per million of free chlorine. So instead of adding three gallons of the pool to bring it to 20 parts per million, you would add about seven gallons to bring it to 50 parts a million. Just double that. If you double the three gallons to bring it to 20 parts a million, that's six gallons, add one more gallon, that'll bring it to about 50 parts per million, and then you really have nothing to worry about as far as not having enough chlorine in the pool at that time. Now, of course, you can't use the pool until it drops down below 10 parts per million, so just remember that when you do shock the pool and bomb it out, that there is a level has to drop to to be safe to swim in. And of course, you'd say something like, Well, you're actually wasting chlorine because you don't really need that much, you just need to bring it to 20 parts a million. But from my experience, I think the air on the side of too much chlorine or more chlorine is much better. If you were to throw in that three gallons of chlorine and it wasn't enough, the pool would zero out or get close to zero again. You'd have to add three more gallons or more afterwards anyway. The pool may start getting some yellow algae and turn green on you or turn really cloudy on you. So I would say to avoid this, always err on the side of much more chlorine than less chlorine in the pool. And you really can't go wrong by putting more chlorine versus less chlorine. There's really nothing that you're going to be able to get an exact number anyway, because like I mentioned, there are a lot of factors in the water that may destroy the chlorine level rapidly. And if you just put three gallons in, and let's just say the phosphate level is at you know 2,000 parts per billion, and you have some microalgae you can't see, it's not going to have any good effect on the pool water in that case, and you wouldn't even know this, unless, of course, you did a phosphate test. And even if you did that, you wouldn't be able to see any kind of microalgae in the pool that's forming in the water. Let me touch a little bit on non non-chlorine shock. The non-chlorine shock is something that you may run into out there, and this shock is potassium monosulfate. You can find it in different brand names and solar different brands, but it'll say something like non-chlorine shock, and it may have, of course, on the back is gonna have the potassium monosulfate as what it what the ingredients are. Now, this is not a sanitizer, so remember this is just an oxidizer, and there are places where the adox oxidizer would be something that you would use in the pool. I like using it before a pool party if customers having a pool party. I have them put a bag one pound in, and then after the party as well. Oxidizing the water is good in a lot of instances because it does break down you know body oils and sunscreen, kind of a little bit like what enzymes do, but it does have an oxidizer. It is an oxidizer, I should say, not an enzyme, but it won't kill algae and it won't sanitize the pool water. The reason I like using it and other pool pearls like using it, is because the oxidizer really helps with the combined chlorine or the chloramines that smell you get, the ammonia smell. So it's a great way to kind of prevent that from happening, especially if there's heavy usage, like a pool party, like I mentioned. And it's something that you would want to put in the pool after or before the party, or both before and after the party. So there's a place for it. It just does nothing for a green pool or pool with an algae bloom in it, and it's not something that I recommend using when you're trying to turn a pool around. It's only useful again with that those pools that have heavy bather use, and you're gonna get a jump start on fighting any kind of combined chlorine that may form in that pool. I think also it's kind of a misnomer when you look at the bag of shock and it says one pound per 10,000 gallons of water. Again, the bag doesn't know the water condition, doesn't know what the water looks like, and there's other factors like circulation and filtration that play into that. There's some other variables, of course, that will play into effect. One of the biggest variables that I think no one really accounts for when you're shocking the pool is the pool cyanaric acid level. And this holds true when you're turning a pool from green that's or that has yellow mustard algae. And the cyaneric acid level does have some effect on the chlorine's effectiveness. We you've probably heard me talk about Bob Lowry's 7.5% formula a lot. This holds true for when you're trying to raise the chlorine level as well. I'll give you an example. Let's say that you get to a pool and you test it, the pool's cloudy and it's kind of murky, the chlorine has zeroed out, and you test the pool, you do a full round of test factors. Now, when you get to the cyaneric acid test, it's coming in above 100. So then you do a dilution test where you take some bottled water, mix it halfway with the pool water, then you do the cyaneric acid test again, and it's coming in well over 200. So there's really no way to know now what the cyaneric acid level is. You know it's over 200 parts per million because the test shows that, and you could do another dilution test. And as you do that more and more dilution tests, the test, of course, gets more and more inaccurate. Most cyaneric acid tests to 80 parts per million or 100 is the accuracy range. Anything above that, it starts to get inaccurate, and then you can do the dilution test to kind of get an idea of what it is. But let's just say it's at 250 parts per million. Well, if it's at 250 parts per million times 7.5%, that means for the pool, the chlorine to be effective in the pool, it has to be at 19 parts per million. And that's 19 parts per million per day to just have some effect on that pool water with the cyaneric acid level at 250 parts per million. So if you are trying to turn a pool around, and again, I'll go back to my 15,000-gallon pool, bringing it to 20 parts per million from zero. That's three gallons of liquid chlorine. But if you have a cyaneric acid level of 250 parts in the water, you're going to have a problem with this formula because that's just the baseline free chlorine level it needs just to be somewhat effective. So you're going to have to go higher than that. That's why I said 40 to 50 parts per million is a pretty safe level to bring it to. And that's why when a lot of pool probes do a green pool cleanup, we don't really test the cyaneric acid because we're just we're we know that if we bring it to 50 parts per million, it doesn't really matter what that level is unless it's at 500 parts per million, I guess. Then you don't have to worry about it. So the cyaneric acid is a factor when you're shocking the pool. And keep that in mind that again, there's a lot of variables involved in it, and it's not just you know one pound of shock per 10,000 gallons of water, one pound of cal hypo, I should say, for 10,000 gallons of water, and to bring it to a shock level takes a lot more than that. And it's one of those things where as you're in the industry and you're learning this, you're going to get much better at judging how much chlorine to add to the pool. Another thing that's not surprising is when you get back there the next day and you put let's say seven gallons of liquid chlorine in the pool, you get back there the next day after 24 hours and you test the water, and the pool showing you know one part per million of chlorine, and you're like, what happened to all that chlorine? Well, a lot of that, hopefully the pool looks a lot better, by the way. So if it was green with mosquito larvae, and you you put you know you brought it to 50 parts per million, hopefully you can see the bottom of the pool at least, or it looks a lot better. And that's because a lot of that chlorine was used up with the what I would say a negative chlorine level, the allergy in there and all the other stuff in there destroying the chlorine. And getting back to the next day and having it at zero, one part per million is not a surprise. If I get back to the next day and it's showing like 10 parts per million, I'm really surprised in a lot of cases if the chlorine actually held to that level because there are other factors like the filtration and how much organic junk is actually in that pool. It's really hard to tell from one green pool to another how much gunk is in there, and raising the chlorine level to a 50 part per million is pretty fair in making sure that you're going to clear out most of that stuff and have somewhat of a chlorine reading, you know, one or two parts per million, hopefully not zero again, but you'll have some chlorine the next day in that pool. Is there actually a hard and fast rule? Like I mentioned, there isn't, but for a green pool cleanup or a pool with a lot of mustard algae, I like the one gallon per one gallon of 12.5 liquid chlorine to every 1000 gallons of water. Seems to be the sweet spot. For those other situations where the pool just kind of looks cloudy or zeroed out, use your judgment on that. But I would, of course, test the cyaneric acid to see where it's at, and then appropriately bring that chlorine level up to a level that's going to be you know 20 parts per million over that cyaneric acid formula that I gave you, 7.5% of the cyaneric acid level. So if the pool has a cyaneric acid reading of 100, you're gonna need 8 parts per million of free chlorine just to make that chlorine effective. And so in that case, I would definitely bring that pool up to about 30 parts per million so that I have that extra 20 parts per million above what would take to make that chlorine effective, if that makes sense. So you're not really doing straight math here, there's no hard and fast formula, but as you're working out there in the field, you're gonna get much better at judging how much chlorine does at the pool. And I would say that if you're worried about adding too much chlorine, don't worry about it. I would be worried more of adding too little chlorine and having to go back there and retreat it and keep adding more and more chlorine to get some kind of effect on it. You really want to go back to the next day, and the pool is gonna look a lot better. Maybe not clear blue, crystal clear blue, but uh you know, murky, milky blue is better than a green pool. And if you had yellow algae, if you get back to the next day and half of it's gone, that's a good sign as well. I'll end by talking about using pool RX or other enhancers to help with the green pool cleanup. And I think it's really effective or yellow algae, mustard algae blooms to have some to test the phosphate level for sure. If there's algae in the pool, there's probably phosphates in the pool at a pretty elevated level. Testing that really helps, and adding a phosphate remover could be part of the treatment. Enzymes can also help. Polar X is a great way to clear a green pool or algae as well. The minerals will help destroy the algae in the pool. I would say sodium bromide was something you could use, but you can't find that anywhere, and it's it's really EPA has come down pretty hard on sodium bromide, so the yellow trin and yellow treat, you can't find those readily, but that's what we used to use in the old days. So switch over to pool or x or another algecide. The algacy will really help accelerate this process, and you can do it with just pure chlorine, of course, but with an algiside or a pool or x or a phosphoryl remover, this does help a lot and make it makes it a lot quicker, and it makes the chlorine much more effective when you're doing a green pool cleanup or a really bad algae outbreak. Using these enhancers really help a lot. If you're looking for other podcasts, you can go to my website, swimmingprolearning.com, and you can find on the banner. You can see a podcast icon. Click on that, there'll be 1900 podcasts you're listening to there. And if you're just in the coaching program, you can learn more at poolguycoaching.com. Thanks for listening to this podcast. Have a great rest of your week and God bless.