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Let’s start with a significant fact: ozone has been used as a pool sanitizer by DEL since the 1970’s. But despite ozone’s longevity, in 2021 there are still misunderstandings about the use of ozone to keep a pool or spa clean. There are questions not only about application—how to use ozone—but also about whether ozone even “works” to keep a pool clean.


Why is there still so much confusion? It’s hard to say definitively, but there are a few typical reasons why 40 years later, not everyone trusts ozone for a pool.

  • Ozone wasn’t always available for everyone. Like lots of tech, ozone used to be much more expensive for the average user. Systems for backyard pools probably weren’t attainable until at least the ’90s for most people. But that still has been 30 years (sorry millennials). Which brings us to . . .
  • As ozone became more common, more manufacturers entered the market. 
    • Overall this is a very good thing—it’s part of what helps the price to come down. But with more players, every system was not created equal. 
    • As tech advances, some suppliers continue, even today, to use very old tech like UV-based ozone. This prevents every user from really experiencing the full benefits of ozone in the pool. And this leads to the last common problem . . . 
  • As systems become more diverse, some manufacturers rely on inconsistent information to sell the “benefits” of their product. This last one is where a ton of the ozone “myths” come from. As competition tries to get a leg up, it can be easy to trash the “other guy’s” system. But all this really does is trash ozone as a technology. So it’s no wonder that a homeowner or pool pro, already doubting if ozone even works, would believe these myths and abandon ozone altogether. 

Here is our promise to you. We think our products are really great—among the best sanitizer systems for a backyard pool. But above all else, we believe in what ozone can do and we believe in safe, clear pools for swimmers in 2021. Our goal is that you get the best info possible so you can make a smart decision about keeping the pool clean.

Ozone may feel confusing but it doesn't have to be scary

Ozone may feel confusing but it doesn’t have to be scary



Let’s start with an easy one. This question we can answer with simple science. Ozone is a volatile gas and a form of oxygen. The oxygen we breathe is O2. It is a stable molecule formed from two oxygen atoms held together by a covalent bond, and well, it keeps us alive so that’s nice. 

Ozone is O3. This molecule is formed from three oxygen atoms and boy is it mad. This triatomic molecule is unstable and wants to get back in balance (go back to diatomic). To do this, the O3 attempts to react with anything it can. And when we say react, we basically mean explode. 

This “explosion” reaction is called oxidation. Oxidation can be very powerful. Not only does it clean in the most basic sense, it can destroy other molecules. This is how we harness ozone in the pool. Ozone destroys bacteria, viruses, organic compounds, algae, biofilm, chloramines; anything it can get its hands on, really. 

Ozone destroys things that chlorine can take hours or days to break down. This reaction is way more powerful than even chlorine shock. In fact, it can pretty much replace the shock in your pool. This is how ozone keeps a pool clean and reduces the amount of chlorine you use.

The ozone generation process is just natural

The ozone generation process is just natural


An ozone system on the pool technically creates ozone gas and injects this gas into the water. The goal is to transfer as much ozone as possible to the water. Some of it may not mix and this will “off gas” into the air. 

Here is the good news: the amount of ozone produced by residential backyard systems is not high enough to be a danger when it gasses off from the pool. Neither OSHA nor the EPA require these systems to capture or destroy the ozone. 

Some commercial systems that produce high amounts of ozone DO have extra safety equipment to prevent leaks, monitor ozone in the air, maximize the transfer into the water, and capture any escaped ozone. CMP provides Mixing De-gas Vessels with a carbon destruct to stop any ozone gas-off. But an MDV is optional for almost all pools and not a requirement. More on that below.

All those bubbles don't have to be a bad thing

All those bubbles don’t have to be a bad thing

Hey, guess what? We made a whole video with ozone experts that answer some of these and other questions. You can check it out here on the CMP Youtube Channel.


This is a really common and sort of tough question. Not that tough, just not straight-forward. In the simplest sense, yes, ozone can break down chlorine. But it’s not that . . . simple.

Ozone doesn’t destroy chlorine easily. Especially the killing form of chlorine, hypochlorous acid. Long before ozone “attacks” chlorine, it will be kept busy by other contaminants in the pool. It’s a path of least resistance. 

The ozone will react faster with whatever is easier to react with. Ozone will react more quickly with a hypochlorite ion. This is the less effective form of chlorine formed when the pH is too high. But a properly managed pool won’t suffer from this issue.

So yes, if the pool has zero contaminants (probably not going to happen) and has a high pH, ozone may react with chlorine. But really it’s not an issue. We do recommend injecting ozone after your chlorine systems to minimize any possible effect on the chlorine. But that’s just best practice, not a revelation that ozone was destroying all the chlorine.


There are some claims that UV will destroy ozone and make it ineffective. These comments have been made relative to ozone in general and AOP systems. Here are a couple ways to tackle that question:

  • UVA is non-reactive with ozone. UVA is the type of ultraviolet that penetrates our atmosphere and gives you a sunburn. 
  • UVC can react with ozone. This is what is inside a DEL AOP system. UVC does not penetrate the atmosphere. If it did we would be in serious danger! So no effect on ozone in the pool.
  • What about the UVC in an AOP system? Let’s get technical: the First Law of Thermodynamics tells us that matter isn’t destroyed, it is only changed. UVC does not “destroy” ozone. It reacts with ozone and as a byproduct creates hydroxyl radicals. This is the Advanced Oxidation Process and an excellent, powerful way to keep a pool clean. But…that’s another post. 
UV-A may toast your skin but it won't react with ozone

UV-A may toast your skin but it won’t react with ozone


In an AOP system, the UVC bulb reacts with the ozone to create hydroxyl radicals. As detailed above, the UVA we are exposed to outdoors does not react with ozone, so it cannot create hydroxyl radicals to treat your pool. 


A residual in a pool is designed to remain available in the water at all times to protect swimmers in the water, among other things. Chlorine is an amazing residual that lasts a very long time in balanced pool water. 

Ozone can exit into the pool and leave some residual. However, this residual is very short-lasting, hard to control and only around when the ozone system is running. At best ozone has a half-life of just 12 minutes in typical pool temperatures. 

The truth is ozone does most of its work in the pipes before it even makes it to the pool. Practical residential ozone systems aren’t going to output a high enough ozone amount to maintain the residual at a meaningful level. Commercial systems are so costly, it’s really not practical to consider this as an option for backyard pools. For this reason we recommend you keep chlorine as your residual. (But ozone can replace your chlorine shock treatments!)


CYA is cyanuric acid, and it’s used in pools to protect the chlorine from being broken down by UV. (Unlike ozone, chlorine is affected by sunlight). However, as CYA gets too high it can sort of “lock-up” chlorine. The chlorine is less reactive, which means more is needed in the pool for it to be effective. 

Many ozone users like to keep their chlorine levels lower, but high CYA prevents this. If you do the math, high CYA may require chlorine levels of 5 ppm or more! For this reason low CYA and low chlorine tend to get coupled with ozone or AOP.

However, the CYA does not directly affect an ozone or AOP system. This is more of an issue with conflating two different, but related, pool care questions.

When in doubt, look to commercial pools!

Most of what we are discussing applies to residential pools that are highly unregulated. But commercial pools are very regulated, inspected and constantly tested. So what can we learn from these installations?

The CDC and MAHC recommend certified ozone systems for high-risk pool environments! In some cases, they are absolutely required (either ozone or UV). So for such highly regulated bodies of water, we have to ask. If ozone didn’t work, would it be required? If ozone destroyed the chlorine, would they even be allowed in commercial pools? 



There are a ton of questions about how ozone is produced. This is one of those areas where sadly, questions often arise from different companies trying to “one-up” each other. We will do our best to set the record straight.

UV-based ozone uses a bulb tuned to a particular wavelength that will create ozone gas. CD ozone (corona discharge) uses an electrical current to do the same thing. If you have ever smelled a thunderstorm, that is ozone in the air created by lightning.

CMP is well-positioned to speak on both options, because DEL used UV Ozone into the 90s and then made the switch to CD ozone. Yep, over twenty years ago. So why the change?

The switch started with commercial-grade systems from DEL. These larger systems used CD ozone to create more of the sanitizer. Not only that, we found they lasted longer and had a stable output over a much longer period. 

Pretty quickly DEL set out to miniaturize this commercial tech into a residential system. This eventually became Advanced Plasma Gap (APG). And yes, we patented that!

It turns out CD has quite a few advantages over the twenty-year-old UV tech:

  • CD produces more ozone per unit than UV
  • CD takes up much less space than a UV bulb
  • CD is more durable and harder to break than a UV bulb
  • CD systems have a longer life, versus UV which degrades steadily over a set number of hours.
CMP has ozone systems for any size residential pool, plus commercial too!

CMP has ozone systems for any size residential pool, plus commercial too!

So why do some manufacturers continue to use UV-generated ozone? Only they know for sure, but the technology is simpler to produce without advanced expertise. CD ozone is innovative, miniaturized technology. Many manufacturers just aren’t prepared for that investment when they can just grab UV bulbs “off the shelf” for their systems.


Every piece of tech has its ups and downs. A corona discharge system can build up nitric acid in high humidity. Output can also decrease in high temps. So what does this mean, really?

Nitric acid buildup may mean you have to replace the ozone feed tube every year or so. But this is pretty easy. And what about the decrease in output? Well, here is the really good news. 

Even when degraded by humidity, CD ozone output is so much higher and more stable than UV ozone, the output is still more consistent than the UV bulb. Whereas the UV bulb output will decrease every day it runs, no matter what you do!

Oh, and one more fact. DEL has continued to improve the design of our CD systems—it’s not like we are still on generation one. While UV bulb systems aren’t a lot different than twenty years ago, our CD systems have less nitric acid buildup and perform even better in high heat than in the past. There is really no comparison.


Nope. The MDV is great at getting maximum ozone transfer in the water while capturing any undissolved ozone and destroying it. But as noted above, at residential system levels this isn’t always required. So, when would you want to consider an MDV? There are a few common reasons:

  1. Some vinyl liners may fade around the ozone outlet. This will vary by pool and by liner. You can also locate the output in an area where any fading is not prominent. BUT if you are concerned, an MDV will fix this issue. 
  2. If a pool has an auto-cover and spends a lot of time with the cover on, ozone can build up underneath and degrade the cover. Now, we would generally advise you to minimize how much time the cover is on when chemicals and ozone are active, as this is always bad for the cover and the pool. But we understand not every pool is the same. So if you like keeping the cover on, you may want to consider an MDV.
  3. Bubble, bubble, toil and trouble! Like we said, every pool is different, every homeowner is different. And some people just do not like the tiny bubbles in the pool. Personally, we like that little fizz but if you aren’t into it, an MDV will pop those bubbles.

As a side note, we’ve heard through the grapevine that some customers have been told our systems require an MDV because we produce just too much ozone. Well, first off, as we noted above the MDV is not required. As far as what is too much—let’s continue that discussion below.


We will be honest—we have struggled trying to answer this question. Certain competition claims their UV bulb systems are better because we produce too much ozone. Weird flex, but OK.

Here is our perspective. Our systems are designed for residential pools. And at that scale, you generally want as much ozone as is appropriate for your pool or spa size to keep it clean. This is not output at the level of our high-end commercial systems, it’s the *right amount* for a backyard pool. This lowers your chemical use, it makes the pool safer, and of course keeps the water clear. Why wouldn’t you want  . . . more?


It is frankly amazing that ozone systems have existed for so long, but are not standard on almost every pool. We really believe that an ozone or AOP system can make every pool better and safer. It’s why we always say we believe the Complete Modern Pool™ is chlorine plus a second sanitizer. And we really mean “modern.” This is the way to do it in the 21st Century!

We understand why you might be hesitant. It’s normal to have questions or concerns. Ozone is an extra system to add to a pool, and whether you’ve built pools for 30 years or owned a pool for a year or somewhere in between, it may feel like just one more thing.

But this is our pitch. Ozone is a simple but powerful chemical. Whether on its own or combined with UV in an AOP system, it will make any pool a better, safer place to swim. Not to mention keeping the water clearer while reducing chemical use. It may not make the pool chlorine-free but it WILL make the water FEEL like it is chlorine-free.

If you never came around to ozone, or if you tried it and dropped it in the past, this is the perfect time to try again. We recommend you start with a DEL Ozone system—we have three residential sizes based on the pool volume. From there you can even upgrade and try out AOP. We 100% believe if you try it, you will love it.

Check out all CMP Ozone and AOP products.

Still have questions? Contact our team below and get more answers. Or check out more of our content below and you can be an expert on ozone yourself.


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