Rookie Pool Chemistry Mistakes Pt.1 – Bob Lowry

Algae keeps coming back even when your test reads “plenty of chlorine”? Here’s the missing piece: cyanuric acid quietly ties up most of your free chlorine, leaving only a small slice as active HOCl. We dig into the real chemistry behind clear water, then translate the math into one simple rule you can use on every stop.

We walk through the practical percentage target that actually prevents algae: set free chlorine to 7.5% of your CYA, or drop that target to 5% when you run borates at 50 ppm. You’ll hear why pools with 150–200 ppm CYA can still turn green at 6 ppm FC, how pH shifts HOCl to weaker OCl−, and why weekly shock isn’t a strategy. If you’ve ever fought a trichlor-heavy pool through summer and wondered why “within range” fails, this conversation gives you the framework to fix it.

We also unpack LSI fundamentals to predict scale and corrosion, then explain why balance on paper isn’t enough if the pool won’t stay put between visits. Targets beat broad ranges: tune alkalinity to control pH rise, maintain appropriate calcium hardness, and let borates smooth pH swings so sanitizer stays effective. By focusing on stable set points instead of chasing numbers, you protect plaster and equipment, reduce callbacks, and keep water reliably clear.

• CYA binding lowers active chlorine and HOCl
• The 7.5% of CYA free chlorine rule
• Borates at 50 ppm reduce the FC target to 5%
• High CYA pools need higher FC despite “good” tests
• LSI as a prediction tool, not a cure-all
• Targets for stability versus chasing ranges
• Balance that holds week to week, not just on paper

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Chapters

• 1:51 Best Of Bob Lowry Setup
• 2:59 The CYA Problem With Chlorine
• 4:28 How Much HOCl Actually Kills Algae
• 6:58 Reversing The Math To A Simple Rule
• 10:15 Borates Lower The Chlorine Requirement
• 12:42 Sponsor: Insurance Offer
• 12:49 Field Reality At High CYA
• 13:51 LSI Basics And Misconceptions
• 16:29 Targets Versus Indices
• 17:57 Balance Versus Stability
• 18:27 Resources And Closing

Transcript

SPEAKER_00: 1:03

Welcome to the Pool Glaid Podcast Show. In this episode, I'm going to do a best of Bob Lower. We're going to do part one of two of some rookie chemistry mistakes you can make if you're learning how to do pool service or if you're taking care of your pool. These are some mistakes you can make with chemistry. And it may not be completely obvious, and Bob Lower is going to unpack some of these common mistakes in part one here. 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. Let's uh talk about some rookie mistakes out there. Now there's a lot of new people in the industry, or you may be an employee coming on to a pool company, and we'll go over some of the top mistakes I think people make in the industry when they first start. And I think number one, and this is also happening even with the old school guys out there, is not understanding the effects of high cyaneric acid on chlorine. And then on the second part of that, you know, how important the cyaneric acid and free chlorine ratios are, and it's something that a lot of people don't consider. And so they'll have a trichlor pool that has cyaneric acid of maybe 150 or 200, and they're getting algae in there every week, and the free chlorine levels at you know five or six parts per million, and they're scratching their head thinking, hey, there's tons of chlorine in here. Why am I still getting algae in this pool? So you want to go over kind of this misunderstanding that happens out there?

SPEAKER_01: 2:44

Yeah, it for years we used to just put in two to four parts per million of chlorine in the pool, and that was supposed to be enough. And then every summer we all battled algae and put in algacides and superchlorinate and shock ones a week and all those kinds of things. And and we were doing stuff weekly to bring the chlorine level up to where it would kill the algae. We started figuring out what the problem is. And and about eight or nine years ago, I spent a few hundred hours studying what's what's going on in the pool. And the good news is that because I'm independently wealthy and independent, if I want to spend 200 hours doing something, I don't have a boss telling me I can't do that. So I studied it to find out what kills algae, how much chlorine we need. Depending on who you talk to, we need only between 0.3 and 0.5 parts per million of HOCL in the water. And the some people disagree with the 0.3. I mean 0.03, but everybody would agree that that 0.05 parts per million HOCL will kill algae. So if we know that, then we're able to calculate how much chlorine is in the water if we know how much cyanouric acid is in the water. So we started figuring out how much cyanuric acid, how much chlorine is in the water. And the fact of the matter is, even with only 30 parts per million of cyanuric acid in the water, 97% of all the chlorine that's in the pool is bound to cyanuric acid. It's attached to it. And it's not like it's not available, but it's not available right now. Only the 3% that is not bound to the cyanuric acid is available for killing anything. That is an equilibrium reaction, 97% and 3%. So if you use some of the 3%, some of the 97 will switch over so that that 97 and 3% is maintained. But because we know that 3% of the chlorine is doing the work, we can multiply the 3% of the amount of chlorine that's in the pool and find out if we've got enough chlorine. So if you have say two parts per million of chlorine in the pool, if you multiply two parts per million of chlorine by 0.03%, okay, you and you well, let me back up. You also may know that when chlorine is in water, the pH determines how much HOCL is made and how much OCL is made. And the the OCL minus and the HOCL are at 7.5 pH is about 50%. So you've got 50% HOCL and 50% OCL minus. So that means that only 1.5% of the chlorine that's in the water is gonna kill anything. So if we take two parts per million and multiply it times one point five percent, we get zero point three parts per million HLCl. And we said we needed zero point five. So if you're keeping the chlorine level at two parts per million in that pool, you don't have enough chlorine to keep algae from growing. And it is that simple. And if we put in three parts per million of chlorine in that pool, one point five percent of three is zero point four five. That's not quite zero point five, but it's close. So three parts per million might actually work. It's on the maybe on the borderline. And if you multiply four parts per million times one point five percent, you have 0.06, and 0.06 will definitely kill algae. So what I claim in my most of the things I write, two to four parts per million of chlorine that's recommended by PHTA may not always work. And don't believe that if your chlorine level is between two and four, you're good. Because I just showed you that you could have two and not be good and four and be good. So if you're in between there, it doesn't mean you're okay. So instead of having to do the math that way, we reversed it and made it easier for you to f to calculate. And so the the free chlorine level that you need in the pool needs to be 7.5% of the cyanuric acid level. And yes, that means if you've got a hundred parts per million of cyanuric acid in the water, you need 7.5 parts per million of free chlorine. It means that. That's their rule, and actually their rule actually never considered the fact that you would have cyanuric acid in the pool. Because your exposure to chlorine is less with cyanuric acid than without it. For that same reason, only three percent of the chlorine is available. So you're not exposed to four parts per million of chlorine, you're only exposed to three percent of four parts per million of chlorine. So um the thing that you can do to reduce the 7.5 percent is if you add borate to the pool at 50 parts per million, you can lower the 7.5 percent requirement to 5%. And that becomes a much more manageable and easy number. 5% of whatever your cyanuric acid is is how much chlorine you need in the pool to prevent algae. And if it goes below that, then you you run the chance of getting algae. And and we have we've been teaching that for three years. I've written about it now for eight years, and I've also got a book that most of you have probably heard of called Pool Chemistry for Service Pros. And it's a short book of 28 pages, but we recommend in there to keep the level of borate at 50 parts per million and um chlorine level at 5% of that of uh CYA. But that book has now been distributed to 13,000 service techs, and they're doing it, and it's working for them.

SPEAKER_00: 10:56

Yeah, and I would say from field testing and experience, um, you know, if you want to keep your pool algae-free, even with a high chlorine level, um, like I gave that example at the beginning, a 200 parts per million cyaneric acid pool, not unheard of in California, by the way, um, a six parts per million chlorine is not enough to keep the algae out, um, even with borates in there. So um with the borates, you would need 10 parts per million. And so if if the new guy is struggling with algae pools and he thinks he thinks that, man, this chlorine level is off the charts, you know, but I'm still getting algae, that's the reason because they don't understand the formula that you just went over there in great detail, by the way, which I really appreciate that. I like the fact that you reversed it because doing the math forward is difficult for anybody, and using that easy percentage backwards is is much better. Um, and then another aspect is the LSI. Interesting, I was talking to um Scott Hamilton over at um United Chemical about his Hamilton index, and that's another index that you can actually use that one in California pretty effectively because of our high calcium hardness level. Um, but the LSI is pretty much the standard of the industry across the country. And what about the pool guy that probably has never heard of the LSI, never w never thought about it? What would be the problem with someone starting out their pool service business or working for someone and not even knowing what the LSI is? And the Pool Guy Podcast Show is teamed up with UPA to bring you affordable, reliable liability insurance starting at just$64 a month. Get up to$2 million in coverage, and the members of my coaching group get an even lower rate. Protect your business and your peace of mind. Sign up with UPA today by clicking the link in the podcast description.

SPEAKER_01: 12:55

It actually depends. If he if he got one of our books and started using targets, he probably wouldn't need the LSI. But um, if he just started doing pools and he's got all this mishmash of information, um understand that the LSI is a method of predicting whether your pool is going to be scale forming, uh, whether you pool water is going to be scale forming or corrosive or what we say is balanced. And it's a method of predicting whether that will, whether the water will be that way. And you measure uh in the old days, we measured five things and plugged those test results into an equation and got the answer. And now with the advent of cyanuric acid and borate, we now have seven things to check. We most of the time look up the seven uh water tests. Uh, we look up a factor for each one of those uh test results and enter them into an equation, and the the desired result is to come up with a 0.0 answer. And that means your water is perfectly balanced, neither scale forming nor corrosive. It is important uh, if you're going to be maintaining the water, to know if you're gonna be forming scale or or not. And there are various indices out there, and frankly, the Hamilton Index is not an index. Um they call it an index, but it's not an index. And it pretty much does only work in California and Arizona. Um most of the other countries can't use it. Um but uh and if you if you use the Hamilton Index and use some numbers from his index and plug them into the LSI, you find that it's not balanced water. Um so I'm not a big fan of the uh Hamilton Index, although it's been around for a long time. But just because it's been around doesn't mean it's a great index. Um but in any case, if you want to follow it, it's better than not doing anything. So um I would suggest just using targets as we recommend for everything. And then you really don't need to be using any index. You just everything is on target or it's not. And if you don't put it on target, you're gonna have a problem.

SPEAKER_00: 15:40

Yeah, it makes sense, and I I think that that's a good answer because your target ranges, and I'm you know, more and the more and more I look at it, and I use this example with you. If you go into the bank and you tell a teller, you know, I like to get$100 out, and she says, Well, here's 80, you know, it's within range of a hundred, you're gonna walk out of the bank not quite as happy. And so the targets make a lot of sense because you're talking about you know, a hundred thousand, two hundred thousand dollar investment in some people's backyards with their pool, and you have all these ranges. And you mentioned before in a different recording that if the LSI is could be perfectly balanced in those kind of ranges that people are using, you know, 80 to 120 for alkalinity, pH of 7.4, and it may not even be balanced.

SPEAKER_01: 16:26

Well, you can balance the water so that it you have a perfect LSI, but still not have a stable pool. And that that is the problem. And you could, you know, you could balance a pool. For instance, if you had an alkalinity of 140, uh, you could maybe use a a pH of 7.2 with that and and have everything else in the normal ranges, and you'd have a balanced pool. But with an alkalinity of 140 and a pH of 7.2, that's only gonna stay 7.2 for you know, maybe today. You know, tomorrow the pH is gonna be 7.5 or 7.6 or 7.8. Uh an alkalinity of 140 is gonna raise that pH like crazy. So um there's a difference between balancing the pool and making it stable. And the goal is to make it stable so that from one week to the next or one visit to the next, nothing changes, or it changes just a little bit.

SPEAKER_00: 17:32

If you're looking for other podcasts, you can go to my website, SwimPoollearning.com. On the banner, there's a podcast icon. Click on that, there'll be a drop down many of other podcasts, 1800 of them you can listen to at your leisure. And if you're interested in the coaching program, you can learn more at PoguCoaching.com. Thanks for listening to this podcast, the Girls here week, and God bless.