Bob Lowry Explains Chlorine Strength

“99% trichlor” sounds like a mic-drop statistic, but it’s also one of the most persistent sources of confusion in pool care. We sit down with Bob Lowry to untangle what that number actually means, why “purity” is not the same thing as “chlorine strength,” and how the industry’s use of available chlorine (based on a chlorine gas reference) warps the way products get talked about on the truck and at the counter.

We walk through the real chemistry behind the label: what free chlorine is doing in the water, why the comparison standard matters, and how trichlor’s makeup includes cyanuric acid that builds over time. If you’ve ever heard someone say liquid chlorine is “weaker” or tablets are “the strongest,” this conversation gives you the language and logic to explain the difference clearly to clients and techs without hand-waving.

Then we pivot to cal-hypo, especially the idea that it “doesn’t add much calcium.” Bob breaks it down in practical terms you can use in the field: if you add cal-hypo to raise free chlorine, you are also raising calcium hardness in a predictable way, and that matters a lot in hard-water regions. We also compare how different percentages of available chlorine change dosing, why some cal-hypo tablets can require much more product than trichlor, and how to think about true cost per usable chlorine. You’ll also hear where to find Bob’s resources (pci.org and pccti.online) and how we can help you level up your pool service business.

Subscribe for more pool chemistry myth-busting, share this with a tech who still quotes the “99%” line, and leave a review with the biggest pool maintenance myth you want us to tackle next.

We revisit a classic pool chemistry myth with Bob Lowry and unpack why “99% trichlor” does not mean you are getting 99% chlorine in your pool water. We also run the numbers on cal-hypo side effects so you can predict calcium hardness rise over time instead of getting surprised by scaling later.  
• why “99%” on trichlor labels refers to purity, not chlorine content  
• how “available chlorine” is a comparison standard tied to chlorine gas  
• what actually gets added when you use trichlor, including cyanuric acid  
• why cal-hypo steadily raises calcium hardness and how to estimate it with ppm math  
• how different cal-hypo strengths and tablet percentages change dosing and cost  
• a simple spreadsheet method to compare true cost per equivalent chlorine  
• where to find Bob Lowry’s resources and tech bulletins online  

Are you a pool service pro looking to take your business to the next level? Join the Pool Guy Coaching Program. Learn more at swimmingpoollearning.com. If you're looking for other podcasts, you go to my website, swingprolearning.com. And if you're interested in the coaching program that I offer can learn more at folkcoaching.com.  

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Transcript

SPEAKER_00 1:02

And welcome to the Pool Guy Podcast Show. It's been a while since we've heard Bob Lowry's voice, and I thought this would be a good time to put up another best of Bob Lowry. And there was a series where I went through a lot of myths, myths in the industry, and Bob Lowry was, of course, the perfect person to debunk these myths. And in this particular episode, we talked about one myth in particular, and that is that trichlor is the strongest form of chlorine. And it kind of looks like that on the surface because you're getting 99% trichlor and 90% available chlorine. But Bob Lowry will explain why this is a kind of myth in the industry as well. 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,

Why This Myth Won’t Die

SPEAKER_00 1:51

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. And here's one that I hear all the time, and you probably hear this too that the trichlor is the strongest chlorine because it has 99% chlorine. And so it's the strongest chlorine product out there, stronger than liquid, stronger than calhypal, because of that 99% number that's on. Well, probably not nowadays because of the cheaper tablets that are out there that are like 91% or 89%. But still, that percentage throws people off and they think, wow, this stuff is super strong, and the other chlorine not getting my money's worth out of it. What do you say to that kind of myth about that 99% number that's thrown out there?

SPEAKER_01 2:40

Well, first of all, there is no chlorine product that has 99% chlorine in it. And I don't mean to deceive you, but but there are a

Is Trichlor Really The Strongest

SPEAKER_01 2:52

number of ways of stating different things. And part of it has to do with what happened many years ago when they started measuring chlorine. The fact was that when you put chlorine gas in water, that it is a hundred percent chlorine, correct? You put it in water, and so it makes some amount of free chlorine in the pool. And then they use that as a gauge to gauge everything else, how it compared to liquid chlorine. I mean to uh gas chlorine. Well, the

The Gas Chlorine Reference Problem

SPEAKER_01 3:29

fact of the matter is, you chlorine gas is two atoms of chlorine. When you put it in water, one atom of chlorine makes HOCL. The other atom of chlorine makes HCl without the O in it. And HCl is acid. So one of them makes the killing form of chlorine and the other one doesn't. But they assigned it a value of a hundred. Okay, so chlorine gas is a hundred percent, even though in reality it's only fifty percent. And as a result, when you compare everything else, they literally have to double it so that they can get the comparison correct. When a label says, first of all, it's 99% chlorine, what they are referring to is that it is ninety-not of that chemical product, the the whole word. That's not the amount of chlorine in it, it's 99% pure trichlor. And somewhere on the label it will say that it provides available chlorine of 90% or 92% or 91.5 or something. Most of them are between 90 and 92. Some might say 93. But it is basically 99% pure trichlor that provides about 90 to 92 percent available chlorine. And the word available chlorine is on the label because that's how it compares with a pound of gas chlorine. When you see a label that says it provides 90% available chlorine, what that actually means is that it's 45% chlorine, 45% chlorine, and 55% uh cyanuric acid. And that's the way it's made. And when you see a label that says that it's 65%, then it's it's actually 32.5% chlorine by weight. But when you put it in water, as it compares with a pound of gas chlorine, it

Purity Versus Available Chlorine

SPEAKER_01 6:09

provides 65% of what a pound of of gas chlorine does. When you see 99%, it is referring to the purity of the ingredient and not the amount of chlorine that's in it.

SPEAKER_00 6:25

Yeah, and I think that's a big thing that people miss when they see that label because they automatically correlate that pure trichlorine as being that powerful chlorine.

SPEAKER_01 6:38

Technically, you could say if you saw calhypo, it could actually say 99% calcium hypochlorite. Yeah. And then somewhere else on the label, it will say provides 65% available chlorine.

SPEAKER_00 6:53

Got it. Makes perfect sense. I mean, if you if you analyze what you just said there, it makes perfect sense, but it takes a little bit of thinking. And people don't do that, they just read the label and they assume that, you know, opposite of what you just said there. And then this last one, I think you touched on it when we talked about how liquid chlorine adds salt to the pool. But I hear this all the time that calhypo doesn't add a lot of calcium to the pool in the scheme of things, because you're only adding a small part per million of it, and you know, it's it's not a big deal to use cal hypo. And cal hypo is really big in Florida, and it was big here in California for a while. I think it's pretty big in Texas as far as using Calhypo. I think they even make cal hypo in Texas there too with the dichlor. So Calhypo, just to clarify, it does add a good amount of calcium to the pool over time, over usage. If you're adding, let's just say the pool tech is taking care of a pool and they're adding two pounds to a pool a week, 15,000 or 10,000 gallon pool, they're adding a lot of cal hypo there, or even

Cal Hypo And Calcium Buildup

SPEAKER_00 7:55

the cal hypo tablets that are slow dissolving. What's your take again on that the calcium being added by Calhypo?

SPEAKER_01 8:02

Probably the best way to explain it, as we have with explaining about trichlor. The best way to explain it is each 10 parts per million of chlorine that you add to the pool. That way we don't have to say a pound in a 10,000 gallon pool or pound in a 15,000 gallon pool, what size is a pool? You know, this way we're saying for each 10 parts per million that you add to a pool, you're going to add seven parts per million of calcium. And you can figure it out yourself. So if you put in a pound of of Calhypo and it gives you six parts per million, and you add another part and it gives you then twelve parts per million, you've increased the the calcium level by about eight parts per million in your pool. So you can figure it out from that.

SPEAKER_00 9:26

Yeah, and so if you're in California where the tap water is like 400 parts per million of calcium already, right using Calhypo, I think one reason why it's not super popular here is because the pool tech noticed right away that you're getting a you know a calcium ring and you're you're adding a lot of calcium to the pool. Maybe in Florida, I think their water is a lot softer. The calcium hardness is not nearly that coming out of the tap. Yeah. But in areas like California, I don't really use a lot of it. I mean, I'm using it this season because I can't find liquid. Um, but on a on a regular basis, I don't really use cal hypo as my go-to sanitizer, mainly for the fact that you know all the pools are at four or five hundred calcium hardness already.

SPEAKER_01 10:07

And I I understand that. And I think that you should also understand that there are five or six different percentage of of available chlorine of calcium hypochlorite products, and I have seen them as high as 75%. Most commonly, when it's in the 70s, is 73% cal hypo. I've seen 65% cal hypo, I've seen 48%, I've seen 43. And I think that the calcium ipochlorite tablets, the new ones, not the old ones, the CCH kind of tablets, but the the new tablets that are out there are about 48% chlorine. And that is meaningful because you're gonna have to use more of it

Percent Strength And Tablet Tradeoffs

SPEAKER_01 11:04

because it's only 48% versus say 90% for trichlor. So, and that was the purpose of them making those percentages, is so you can do some comparisons. And the comparison is that if the label says it's 48 and the label says it's 90, you're talking about one being almost twice as more as the other, pound for pound. So if you put in a pound of one, you need two pounds of the other one to make up to form them to be equal. So it's a way of comparison. The and the part that isn't chlorine is something that's gonna end up either as TDS or calhypo. So my my suspicion is that the 48% probably has about the same amount of calcium in it, but then the rest of it is is chloride and sodium. So you're gonna increase TDS and calhypo.

SPEAKER_00 12:05

And what uh you mean in calcium, right?

SPEAKER_01 12:07

I and calcium, I'm sorry.

SPEAKER_00 12:09

I can I can pretty much tell you that's true about adding more of the cal hypotablists equal trichlor. And my testing, I'm gonna say that four cal hypotablets is about equal to using two trichlor tablets in a pool. And the cal hypo tablets are pretty expensive. So if you're gonna switch to cal hypotablists, you know, budget for that because they're not cheap tablets to use in your pool, and you have to use probably the double amount that you would use for the trichlore. The only benefit of the cal hypotablets, I think, is there's no stabilizer or cyaneric acid in them, but they are they are pretty pricey, and mainly because there's only one one or one manufacturer that makes that so dissolving cal hypotablet.

SPEAKER_01 12:53

Right. I did make a an Excel spreadsheet that I've given to practically anybody that wants it, that you can put in the size container that you buy and the amount you paid for it, and it will calculate the amount of money for the equivalent of a pound of pure chlorine. And then you can do it for each of the kinds of chlorine and figure out which chlorine is the cheapest for you to use. And it's just a little small spreadsheet. I haven't been able to figure out how to get it on my website so it can be downloaded for free there. If you have a method or something, I'd be glad to give it to you so you can distribute it to your to your listeners if you'd like.

SPEAKER_00 13:46

I can definitely, if you send it over to me, I can definitely put it

Cost Comparison Spreadsheet And Resources

SPEAKER_00 13:48

on my site on your pages, on your pages where you have your your information. Again, your website, pci.org, has a lot of your tech bulletins that you write. It also has pctti.online. Yeah, pccti.online. Yeah. It can be confusing. These websites with the the dot whatever now gets really confusing. But thanks again for your time on this. And I I think the what if one was kind of interesting because it answered a lot of questions for people. And these common myths definitely are necessary to unpack because they get propagated out there and then they just become kind of truth in the industry in some way, just like the one that I hear. I've heard probably for 30 years now that you can't use chlorine in a in a hot tub that's using bromine tabs. We've debunked that one in a previous episode before, too. And that's been around since I started Pool Service. I don't know where that one came from, and I hear it from everybody, and I even get comments sometimes that's like, hey, you can't use liquid chlorine in a hot tub. And so these things turn in the truth in a way. You don't you don't spend time debunking them. So again, I thank you for that. And the listeners really appreciate all the information you give them in these podcasts. This is the most popular series that I have, all the ones that I have with you. If you look at the numbers of the most popular

Why Debunking Myths Matters

SPEAKER_00 15:08

podcasts that I have recorded, and you know, your your big personality in the industry, whether you think you are or not, people like your material and they quote you everywhere now. It's like, as Bob Lowry says, so I hope you appreciate or feel honored by the quotes from people that they preface everything by saying Bob Lowry says this. So that you know that that means something to someone in the industry for as long as you have been in it.

SPEAKER_01 15:32

Well, I've been around a long time. You know, in my career, I've gone from who is he to he's a a jerk to he's a an idiot to I think he's crazy. Is he really a chemist? I've I've heard practically everything from he's a maverick to to all kinds of things. And probably in the last two to five years, I've gone from being a maverick to being a genius. That's funny. You know, it's it's one of those things where, you know, I wrote a whole book about pool chemistry, and if you look at the CPO manual, there's there's 34 guys with PhDs that wrote that book. And and there's one of me. You know, and and so I've got all of that knowledge, and and I've been able to pass it along to people, and I'm glad to do it.

SPEAKER_00 16:32

Yeah. Well, again, we appreciate your time. And I don't know how many of these we recorded, but we'll keep going as long as you want to keep recording them and putting them out there. And so I wish you the best over there in Peru. All right. If you're looking for other podcasts, you go to my website, swingprolearning.com, where I have over 1900 podcasts for you. Just click on the podcast icon. You can listen to those at V Sure. And if you're interested in the coaching program that I offer can learn more at folkcoaching.com. Thanks for listening to this podcast. Have a good rest of your week and God bless.