Bob Lowry Explains Trichlor Tablets and Pool Acid Cautions

Think evaporation lowers cyanuric acid? Think again. We open the cover on persistent pool myths with help from the late Bob Lowry’s clear, data-driven explanations, and show how small assumptions can create big chemistry problems over a season.

First, we break down why CYA never leaves with evaporation—only pure water does. That means every trichlor tablet quietly stacks CYA week after week, often hitting 100 to 150 ppm in a single swimming season. We compare sanitizer byproducts in plain terms: trichlor and dichlor raise CYA, liquid chlorine nudges TDS via salt, and cal hypo increases calcium. You’ll hear practical numbers you can use on route, like how a gallon of liquid chlorine typically adds around 20 to 30 ppm salt depending on pool size, and how 65 percent cal hypo can add about 7 ppm calcium for every 10 ppm of free chlorine delivered.

Then we shift to acids. Muriatic acid remains the straightforward choice for lowering pH and alkalinity without adding sulfate. Dry acid, while convenient, introduces sulfate that can accumulate and lead to calcium sulfate scale—harder to remove than calcium carbonate and invisible to the LSI you rely on. We also cover why dry acid needs airtight storage due to deliquescence, how to approach dosing when total alkalinity runs high, and why older warnings about dry acid and salt systems don’t reflect current understanding, even if they persist in some manuals.

By the end, you’ll know how to choose the chlorine and acid strategy that fits your climate, hardness, and maintenance plan. 

• evaporation removes only pure water, not CYA
• trichlor adds 6 ppm CYA per 10 ppm chlorine
• CYA rises 25 ppm per month at common usage
• water loss from draining or splash removes CYA
• liquid chlorine adds modest salt and TDS
• all chlorine types end as part of TDS
• cal hypo adds about 7 ppm calcium per 10 ppm FC
• dry acid introduces sulfate and hidden scale risk
• calcium sulfate scale does not show on LSI
• dry acid is deliquescent and needs tight storage
• high alkalinity often n

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Chapters

• 1:50 Remembering Bob Lowry
• 2:38 Coaching Program Invitation
• 2:38 Myth Setup: Trichlor And Evaporation
• 3:17 Why CYA Never Evaporates
• 4:05 How Fast CYA Accumulates
• 4:53 Water Loss Versus Evaporation
• 5:24 Liquid Chlorine And TDS Reality
• 6:48 All Chlorines Add Something
• 8:31 Cal Hypo And Calcium Buildup
• 10:33 Are All Acids The Same
• 11:27 Sulfates And Hidden Scaling Risk
• 13:45 Handling Dry Acid And Storage
• 14:37 Acid Dosing And High Alkalinity
• 16:38 Acid Magic, SWGs, And Old Guidance
• 17:55 Final Cautions And Resources

Transcript

SPEAKER_01: 1:02

Hey, welcome to the Pool Way Podcast Show. It goes without saying that Bob Lowry had so much knowledge in the pool industry, and I got the privilege of recording many, many podcasts with him over the course of a two-year period before his health started failing, and of course he passed away. And you're gonna really enjoy this one here where he talks about trichlor tablets and the differences in pool acids. 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. Let's jump to the common chemical myths that you hear out there. The first one that you hear, some of the common chemical myths that you hear out there. Um, one of these is trichlor tablets, don't add a lot of cyaneric acid to my pool because I get a lot of evaporation in my area. We'll just take California as an example. In my area, I would say I'm losing about an inch, maybe an inch and a half a week when it's you know during the summer. And so people will say, well, since I'm adding fresh water to the pool, the trichlor tablets aren't adding as much cyanaric acid as they normally would be if it wasn't evaporating. I hear that a lot. And what do you say to that myth?

SPEAKER_00: 2:29

Well, the myth is that that you think that that cyanuric acid evaporates and it doesn't. The process of evaporation is like the process of distilling. Only pure water evaporates out of the pool. All of the calcium, all of the TDS, all of the chlorine, all the stuff that's in the water stays there and the pure water evaporates. Everything else stays behind. So as you add cyanuric acid from the tablets, it builds up. And as you use chlorine, the chlorine becomes chloride in the water, which is salt and part of TDS. So all of it eventually becomes a solid in the water that can or can't be a problem. But cyanuric acid builds up. And as I've said in another podcast, the the amount of cyanuric acid is for each 10 parts per million of chlorine added by trichlor, you get six parts per million of cyanuric acid. And if you're using 10 parts per million of chlorine a week, your cyanuric acid is going up by six parts per million per week or 25 per month. Or if you've got a swimming season in the that's five or six months long, you're looking at the cyanuric acid going up 100 to 150 parts per million in one swimming season.

SPEAKER_01: 4:02

Yeah, which is a lot. It's huge. Um so the only way it comes out of the water is with you know backwashing, partial draining, maybe splash out from a lot of pool use.

SPEAKER_00: 4:13

Yeah, it's it's it's only it's only from water loss. Whether you intentionally drain it, bather drag out, splash out, or a leak. But in any case, uh it's because you've lost water, but not because of evaporation.

SPEAKER_01: 4:29

This makes total sense. And I think people have that, I don't know where this comes from, but I hear it a lot. So this one, you know, thanks for clearing that up. And then, of course, if you're not if you don't want to use trichlor, you're gonna switch to an alternate chlorine type. We've talked about this before that all chlorine has a byproduct, and I've heard this a lot too. I don't really want to go to liquid chlorine because that will add too much salt to my pool and raise the TDS level too high. And what do you say to that? That actual when someone says that to you.

SPEAKER_00: 4:59

You're right. Every chlorine has some byproduct or something that it's combined with that gets into the water. And with trichlor and dichlor, we get cyanuric acid. With liquid chlorine, uh, we get salt and and sodium and chloride. Um with calcium, we get calcium and uh chloride. Um, so we end up getting something in the water. In the case of liquid chlorine, we get about 30 parts per million of salt into the water for each gallon that we put in the pool. If it's a 10,000 gallon pool and a 15,000 gallon pool, then you're looking at about 22 parts per million for each gallon. So it's only going to increase TDS by 22 parts per million per gallon. How many gallons are you going to put in that pool? You know, and and if you're putting in a gallon a week, even your TDS is going up by 20 parts per million a week. And at the end of a whole year, you're looking at it going up 50 times that it goes up by a thousand, maybe. But but in the scheme of things, increasing TDS by 1,000 uh ppm means that for the saturation index, it takes 1,500 parts per million to change the saturation index by 0.1. So it's not in a year, it's not doing hardly anything. And don't forget that that other kinds of chlorine, they all add something. And so even when you add uh trichlor and dichlor, all of that is eventually being dissolved in the pool. When you put a pound of dichlor in the pool, it all becomes TDS eventually. Sure, some of it is chlorine right now, but uh when the chlorine is not not chlorine or not HOCL, it goes to being chloride in the water. So all of the chlorine, no matter how you put it in the water, all of it ends up being part of TDS.

SPEAKER_01: 7:31

Yeah, and I think every manufacturer kind of throws the other chlorine type under the bus, so to speak. And so the fact that liquid chlorine adds salt to the pool, I've heard from a I'm not going to name the manufacturer, but this is one of the things they promote in their literature that, hey, you're adding a lot of salt to your pool, you're raising your TDS, and that's why you should use our chlorine type.

SPEAKER_00: 7:52

And uh, you know, so you've got cyanuric acid buildup with dichlor and trichlor, you've got uh salt buildup or TDS buildup from liquid chlorine. If you use calhypo, you got calcium buildup. And just like we talked about the cyanuric acid buildup, the calcium buildup from using uh calhypo is for each 10 parts per million of calcium of chlorine added by calhypo. If it is 65% calhypo, then you're adding about seven parts per million of calcium to the pool. You know, and and uh if you use ten parts per million of chlorine a week, that means your calcium level is gonna go up by seven parts per million per week. So in in uh 10 weeks you're gonna have 70, and 15 weeks you're gonna have nearly a hundred parts per million of calcium more in the pool than when you start it. And that would be in about four months. So, and which is worse over a four-month period to have to have uh four hundred parts per million of TDS or a hundred parts per million of calcium.

SPEAKER_01: 9:32

I think that we'll let the listeners decide that one for themselves. Here's another one that I hear a lot. We know this isn't true, but and we don't I don't know if it's the salespeople in the stores telling them this, but all acids are pretty much the same. Myratic acid, sodium bisulfate, the dry acid, and acid magic. You can use any of these, it's not gonna be a problem. If you can't find muratic acid, go ahead and switch to sodium bisulfate and use that in your pool. That's probably not entirely true because they're all different kinds of acids, right?

SPEAKER_00: 10:07

Yes, they are different kinds of acids, so they're not they're not all equal. So the pH alkalinity adjustment tool lists um dry acid and muriatic acid. It does not list sulfuric acid, but um, and those would be the three common ones would be liquid acid, dry acid, and sulfuric acid. Muriatic is hydrochloric. But um in any case, one of the problems with using dry acid is the fact that it is a sulfate. And adding sulfate to the water uh can eventually cause a problem. And when you get above about 300 or so parts per million of sulfate in the water, you can start to get calcium sulfate scaling. And uh the scale is pretty difficult to remove. It's a little more difficult than calcium carbonate to remove from the pool. So and the other sources of sulfate in the pool are mono per sulfate. So when you add uh oxidizer to the pool, you add sulfate. When you add uh dry chloride, uh dry uh acid to the pool, you add sulfate. And if those things build up, you start to get calcium sulfate scale, and that doesn't show up on the the saturation index that we use. So you can have scale in the pool, even when you think you have a good LSI, you can have scale in the pool, and it's because of the sulfate. And we don't test for sulfate. There are some companies that that have sulfate test kits, but so it is possible to have a problem with that. Sulfate also can be used by by algae as a food source. So even though we may be getting rid of phosphate in the water, sulfate might be something that the algae can use in place of phosphate. So it's not all the same. You know, the goal is to get hydrogen ions into the pool, and and when you add HCl, you add hydrogen ion and chloride ion. When you add dry acid to the to the pool, you're adding sulfate and hydrogen ions. When you add sulfuric acid, same thing, except that it's much stronger. There's more of it. So um so there is that. The other problem with dry acid, and I'm not picking on it, I'm just telling you the reality, dry acid is called deliquescent. And what that means is that it can absorb water from the air and make a liquid out of itself. And you may have noticed that when you take dry acid, if you spill some on the deck, when you come back, it's it's wetter, it's a puddle, and it's absorbed some humidity, uh, some water from the humidity, and and made itself into a liquid. And that that process is called deliquescence. But uh so there is a problem with using liquid, uh dry acid, in that you need to make sure you keep the containers very tightly closed so that no air gets in there with humidity in it.

SPEAKER_01: 13:43

Yeah, and also I think with the dry acid, correct me if I'm wrong, if the alkalinity is higher, let's say 120, 140, you're gonna need more of that product to lower the pH than if you were adding muritic acid to a pool with a high pH, with a high alkalinity.

SPEAKER_00: 13:58

Well, um, yes, you probably would. Um and again, the the amounts of acid that you might need are are listed on the the the those calculations are very complex, by the way. And the the pH alkalinity adjustment tool does over 111 different calculations to try to figure out the amounts of of acid and and uh that you need to adjust pH and alkalinity.

SPEAKER_01: 14:27

Yeah, because I notice on the bucket of if you look at if you actually read the label of the chemical product, which people don't usually do, but I read the whole thing on a bucket of the dry acid, and one of the things it does mention is that um if the alkalinity is really high, use an alternative. I think one of them says use use muritic acid to lower that first, and then you can use the um dry acid to maintain the pH, because I think you have to use more of that product than they want. They don't want people using a ton of that in their pool for some of the reasons you mentioned, I think would be counter to that. And I would say maybe the acid magic would be more more of a direct switch to muratic acid, but it's like three times the price of the bottom muric acid than the acid magic product.

SPEAKER_00: 15:10

It's got some additives and enhancements in it, and and uh, but you do because they put that stuff in there, pound for pound, or you know, volume for volume, you're gonna need more of it, and it's already more expensive. So whether or not you want to use it is, you know, a personal decision. Yeah. Um, there was some information out there about not using uh dry acid with a chlorine generator. I went with I um I explored that and researched that and talked about it with uh Richard Falk. It is not a problem to use dry acid with a chlorine generator. There the directions from I think it's Pentair uh says not to use dry acid with a chlorine generator. And we looked up the original the original document that they saw, and there was a mistake in the document. And so um it's just been passed on forever. But it is okay to use it. But the the the real warning for me is that calcium calcium sulfate scale is a problem in this industry that we don't address. And the more that you increase the sulfate level, the more you have the potential to get scale. And it's not something that we test for or use as part of the saturation index. And so you can get scale despite having a good LSI.

SPEAKER_01: 16:47

So that's a word of caution for those that are switching to the dry acid product that keep an eye on that because that's something that no one really talks about except you. You're the one who first time I heard it too is right here. Um, so that's new information, and I think it's it's vital information that probably should be disclosed somewhere else too, maybe on a labeling or or something. But to get a manufacturer to put it on there is probably not going to happen anytime soon. And if you like this episode, you can of course find more podcasts by going to my website, swimmingpoollearning.com. On the podcast on the banner, there's a podcast icon, click on that, and there'll be a drop down menu with over eighteen hundred 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 rest of your week and God bless.