Bob Lowry Breaks Down the Most Powerful Chlorine for Pools

“Liquid chlorine is weak” might be the most expensive pool myth on the internet. We dig into the real meaning of “available chlorine” and why the percentage on the label can mislead you when you compare liquid chlorine to trichlor tablets, dichlor, or cal hypo. With Bob Lowry guiding the chemistry, we translate confusing terms like weight percent and trade percent into something you can actually use: how much usable chlorine you’re putting in the water.

We also talk about the hidden part of every chlorine choice: the byproducts. Liquid chlorine ultimately adds salt, cal hypo adds calcium, and dichlor and trichlor add cyanuric acid, and each of those can create problems if you don’t plan for buildup. If you’ve ever wondered why your pool chemistry “drifts” over time, this is the missing link between sanitizer choice and long-term water balance. 

Salt water chlorine generators get a full reality check too. A salt pool still uses chlorine because the cell makes chlorine gas that becomes hypochlorous acid in the water. We cover output limits, why incorrect voltage or current can keep a system from producing enough chlorine, why salt residue can be corrosive after evaporation, and why bonding matters more than most people realize. We also clear up a common mistake: boost mode doesn’t shock a pool, so we explain what to do when you need chlorine fast. 

• why chlorine percentages on labels don’t compare evenly across products
• weight-to-weight vs trade percent vs volume-based strength terms
• a simple rule of thumb for liquid chlorine strength per gallon
• why chlorine gas is used as the comparison standard
• how trichlor’s “available chlorine” number gets calculated
• what each chlorine type adds to the water: salt, calcium, cyanuric acid
• how salt water chlorine generators make chlorine gas in the cell
• why low voltage or wrong current reduces chlorine production
• salt level targets and why salt residue becomes corrosive after evaporation
• bonding and grounding to reduce electrolysis risk
• why pH rises in salt pools from sodium h

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Transcript

Coaching Program Quick Invite

Available Chlorine Percent Explained

SPEAKER_00 1:02

Hey, welcome to the Pool Guy Podcast Show. In this best of Bob Lowry. Bob Lowry is going to unpack the strength of different chlorine types. It is the question that's asked often which chlorine type is the strongest, and what chlorine type is the most potent, has the most active chlorine. And Bob Lowry will answer all of this in today's podcast. 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. So I get this all the time. So someone says, you know, liquid chlorine is really weak because it's only 12.5% compared to the trichlor tablets, which are 99% available chlorine. What is the available chlorine percentage? How do you, you know, get it from one from a dry chemical to a liquid chemical or from trichlor to cal hypo? How is that calculated or compared? Because it's really confusing out there in the market. I've even seen manufacturers use their chlorine percentage to kind of beat down the competition.

Why Chlorine Gas Becomes The Standard

SPEAKER_01 2:15

Yeah, there's a a confusing array of terms used when you describe how much chlorine is in a product. What people are used to is what we call a weight to weight percent. So if you put in a pound of something into 10 pounds of something, it's it's 10%. And and so that's the way we are used to hearing things. But then there are what we call trade percent, which is a made-up term, and then there is actually a a volume to volume term, which is not weight to weight. It's a you know a quart of something and ten quarts of something, and it's not weight to weight. So there's different ways of of describing it. But the the practical thing is this the amount of chlorine in a gallon of liquid chlorine is about one pound of pure chlorine, and in uh a pound of trichlor, it is about ninety percent of one pound. So you can either think of it as ninety percent of a pound, or it would take 1.15 pounds to equal one pound, either way. So you can tell from that if something says it's it's 55% available chlorine on it, then that's compared to what one pound of chlorine is. Furthering the confusion is that years ago when they tried to make a a method of comparing chemicals, they said chlorine or pure chlorine, gas chlorine, when you put it in water, makes a hundred percent. There's nothing in it, so it's a hundred percent, right? Well, yes, but what happens is when you put pure chlorine in the pool, it is chlorine gas. And the formula for chlorine gas is Cl2, which means it's two atoms of chlorine. So when you put it in water, one atom makes HOCL and the other atom makes HCl acid. So technically, only 50% of that molecule of chlorine is making chlorine in the pool. The other one's making acid, but they assigned it a value of 100%. So now how do you compare, you know, against chlorine gas, how do you compare it? That's the way it came about, and that's that's we use chlorine gas as a standard, but chlorine gas is technically only 50% of it is making making chlorine in the water.

SPEAKER_00 5:27

So is it safe to say that liquid chlorine compared to calhypo dichlor trichlor has a larger available percentage, but even though it's a liquid, just based on the math that you were saying?

SPEAKER_01 5:41

Yes. Yeah, it makes perfect sense. So the only and that's of dry products. When you get to liquids, it's it changes because liquid is a a a weight a weight percent. So generally we just say there's a pound of chlorine in a gallon. A pound of pure chlorine in a gallon.

SPEAKER_00 6:36

Or 12.5 uh liquid chlorine.

SPEAKER_01 6:39

If it's 12.5 percent, if it's 10 percent, it's it doesn't have a pound. It's like you know, nine-tenths of a pound.

Byproducts Each Chlorine Adds

SPEAKER_00 6:47

Yeah, that's important for people to know the strength of the chlorine. So sometimes they're they can be fooled thinking that certain chlorines are more powerful just based on what you just said. And it is confusing. So even after you explained it, it's still really confusing.

SPEAKER_01 7:02

Well, so uh a little bit further into what we're doing, technically trichlorine, if you actually calculated the molecules in it, technically trichlor is about 45% chlorine. Because we have to compare it to gas chlorine, we literally have to double it. And that's why the package says it's 90% available chlorine instead of saying that it's 45%.

SPEAKER_00 7:51

Basically, you know, for the average person out there, the chlorine that is attached to some product, and you're gonna have a byproduct. You know, liquid chlorine has salt, cal hypo has the calcium, dichlor and trichlor have the cyanuric acid, is that correct? Right.

SPEAKER_01 8:09

So everything is gonna add something to the water that you may or may not have to deal with. Either cyanuric acid, sodium, calcium, something that you're gonna have to to build up or deal with. Yes.

SPEAKER_00 8:28

And let's touch on the salt water generators because they're pretty popular and manufacturers are pushing them with the current trichlor shortage. People think, of course, they're not a chlorine-producing device, but they are.

Output Problems From Low Voltage

Salt Levels And Real-World Salinity

Evaporation Leaves Corrosive Salt Behind

Bonding And Electrolysis Risks

Why Salt Pools Push pH Up

Why Boost Mode Is Not Shocking

More Episodes And Closing

SPEAKER_01 8:42

Chlorine generators, they actually make chlorine gas. But because it's being made in water, the chlorine gas dissolves right away and makes hypochlorous acid. So it technically makes chlorine gas. It also makes sodium hydroxide, it makes hydrogen gas. And so it makes those three things from salt that you add to the pool. And I often hear this we have a salt pool, we don't use chlorine, and that couldn't be any farther from the truth. The fact of the matter is, if you have a salt pool, you're making chlorine. Most of the chlorine generators are capable of making about one pound of pure chlorine per day if they ran 24 hours a day at 100%. One of the things I've recently found out is that the the controllers and all the electronics that are out there, sometimes the chlorine generators not getting the correct current, the correct voltage. And when it doesn't get the correct voltage, then it doesn't make that pound of chlorine. So the the voltage, the DC current that it needs is critical. There is a specification for the cells and how much current they need. And you can also then check it with a meter to see if it's getting the right amount of current. And we had a guy that had a 26,000 gallon pool and he was having to run his chlorinator 100% 24 hours a day, and he was barely keeping up with it. And it wasn't because he was using so much chlorine, it should have been making four parts per million of chlorine per day in that pool. And it wasn't, it's important that you get the right current to the unit. But aside from that, you need the right salt level. If you get too much salt or too little salt, then there's a problem. Also understand that people say, well, you know, the salt water's not good for you, or salt water is good for you, or it's only a little bit of salt, and so on. And the answer is, yeah, it's only a little bit of salt, but the fact of the matter is that it's only one-tenth of what's in the ocean. And the amount of salt that's in the pool is actually very close to the amount of salt that's in your tears. So swimming in it is not like swimming in the ocean. But people need to understand is that when the water goes out of the pool and sits on the deck or handrail or anywhere around the pool, as long as it's still a liquid, no problem. But when the water evaporates away, it leaves the salt behind. And now you have a hundred percent salt on whatever that water was on. Whether it's aluminum, you know, some of your travertine deck or whatever, it's like you took some mortan salt and poured on it. It's corrosive. Bonding becomes an issue. And what I mean about bonding is that you should have a common copper wire that connects each piece of electrical equipment to a ground and not just the pipe that runs in the ground. Better to have it on a stake or rod that goes that's driven into the ground. If you don't do that, because you put salt in the water, it conducts electricity better. And so you can have problems with electrolysis and and and other problems in the pool because it's not bonded correctly. So it needs to be bonded, and you need to make sure that the pool has done that. Because with electricity and the pool and so on, your pool is actually a giant low voltage battery. And if you don't ground it, you know, guess what happens? You know, it's the same thing as leaving the batteries in your flashlight for three years and then opening it up. What do you think it looks like? So it's important to know that. Also understand that the chlorine generator, the pH of your pool is going to go up. And it's going to go up for a couple of reasons. One is it makes hydrogen hydrogen, uh, I'm sorry, sodium hydroxide. And so because it makes sodium hydroxide, the pH goes up because of the hydroxide. It also makes hydrogen gas. And hydrogen gas is a bubble. It's it's an aeration. And and because there's a number of plates in the cell, there's turbulence. So you have turbulence and aeration, and the turbulence and aeration is continuous and it raises the pH of the pool due to CO2 off-gassing. These are some of the things that you need to be aware of. They you you cannot shock a pool with a chlorine generator. If you need to superchlorinate your pool, hitting the boost button, you know, raises the chlorine level up about double over a 24-hour period. That's not shocking the pool. What you need to do, if you need to shock your pool, is take some liquid chlorine or calipo and put it in the pool and get the chlorine level up very fast right now.

SPEAKER_00 14:23

Yeah, we should clarify that that boost mode on the salt generator, all it does is increases the 100% output. It doesn't add any more chlorine to the pool per se. It just increases the output of the system. And if you're looking for other episodes, you can find those by going to my website, swinging for learning.com, where I have over 1,900 podcasts. Just click on the podcast icon on the banner. And if you're interested in the coaching program that I offer, you can learn more at poolguycoaching.com. Thanks for listening to this podcast. Have a rest of your week. God bless.