Ozone: Should You Use It In Your Pool?
In my never-ending quest to make pools easier to maintain, I’ve been experimenting with ozonators. These little units seem to have a lot going for them. I’ve used them on a handful of jobs over the last year and a half or so, and I’m fairly pleased with the results to date: much lower levels of chlorine are needed; no irritating chloramines in the water (as in none whatsoever); and not as much fussing with pH since ozone is pH neutral. As an added bonus, the water looks crisper, brighter, clearer.
As with anything in life, though, there is the downside to consider, too. But to come to grips with the good and the bad of ozone generators, we need to first understand what they are, how they work, and the nature of ozone, especially as it relates to pools.
Ozone
An ozone molecule is three oxygen atoms stuck together, denoted O3. Normal oxygen in the atmosphere is a pair of oxygen atoms (O2). Ozone does exist in the air around us, but isn’t very common. It’s a component of smog — not good — but is also generated by lightning, and is responsible for that wonderful fresh, clean smell after a thunderstorm. The thing that makes ozone attractive for use in pools is that it is a very strong oxidizer, much stronger than the chlorine in the water, much stronger than regular old oxygen (O2) as well.
An oxidizer, you might remember, is a compound that basically burns something up. For example, if a leaf falls in a regular old chlorinated pool, it will be oxidized: after a few days, the leaf will be filmy, translucent, almost completely consumed by the chlorine. That’s oxidation, in this case basically slow-motion burning. Besides being an oxidizer, chlorine is also a sanitizer. It kills the bad stuff in the water, like bacteria, viruses, algae. That’s what makes chlorine so attractive in pools — it’s both a sanitizer and an oxidizer.
Unlike chlorine, ozone is not a sanitizer, strictly speaking. It is just an oxidizer. However, it is such a strong oxidizer that it pretty much accomplishes the same thing. When it comes into contact with any of the previously mentioned nasties in the pool, they are immediately destroyed. For example, if ozone comes in contact with a bacterium, it bursts part of the cell wall, killing it. It operates in a similar fashion on bacteria’s evil cousins, algae and viruses.
Ozone does this because, of the three oxygen atoms it’s made of, two are tightly bound, while the other is attached more loosely. When ozone bumps up against something, say a particle in the water, that third, weakly attached atom breaks free and attaches instead to the particle. The remaining two tightly bound oxygen atoms are now back to their usual, more stable, form — O2. But that oxygen atom that got left behind is the power of ozone for our pools. That’s the little guy who oxidizes the bad stuff in the water.
How It Comes to Be
In the pool industry, there are two basic types of ozone generators: UV (using ultraviolet light to make the ozone), or CD (using corona discharge — electricity, like in a thunderstorm — to create it).
I’ve been using the corona discharge units on my projects. They are advertised to generate many more times ozone than the UV method. I can’t verify this myself, but I can tell you that one major manufacturer (DEL Ozone) no longer makes the UV type, preferring the more powerful CD units instead.
Anyway, both of these methods do basically the same thing: split some O2 molecules and recombine them, making O3. Ozone.
From there, it must be introduced into the pool water. This is most often accomplished by running a tube from the ozone generator to a venturi in the pipe at the pool equipment. (side note: a venturi like this is a funnel-shaped narrowing in a pipe. As the water is forced through this funnel, an area of low pressure is created Where the water comes out of the venturi. That small region of low pressure is where the ozone is sucked into the pool water. Your spa’s jets work the same way.) The venturi mixes the ozone thoroughly into the water, so it can efficiently do its job: kill off the bad guys and oxidize everything else.
The Drawback
The biggest drawback to ozone is also its chief strength: it is very reactive, very volatile. It quickly attaches to and obliterates all types of stuff. But it also means that it isn’t around for very long. In fact, once ozone stops being produced and injected into the water, there is no residual of it left behind. It is consumed extremely rapidly.
To put it another way … when the pump and/or ozonator shuts off, no ozone remains behind in the water.
None.
If we stop and mull this over, something begins to dawn: if ozone is so reactive, then most of it is used up near where the filtered water comes back into the pool, right? Or in the pipes themselves, before the water even makes it back to the pool. So, all the water running through the equipment is free of the undesirable stuff, it seems. But what about other things in the pool, the stuff that isn’t being run through the filter? Stuff just happily sitting there in some far corner of the pool? Like algae, for instance.
Algae colonies often grow on the surface of the pool, the plaster, vinyl or fiberglass. The ozone can get to the top layers, but it has a hard time making it all the way across the pool and then getting to all the different yucky strata and killing them. Yes, algae can be a problem for pools relying on ozone. And all pools will have an algae problem sooner or later.
Which brings us to our next point. If you’re using ozone, it would be prudent to keep a small chlorine residual in the water, as well. This little bit, say 0.5 to 1.0 ppm, is what can keep stuff like those dang algae colonies at bay.
But, if a chlorine residual is required, why even use ozone at all? Why not just say, “The heck with it,” and stick to old-fashioned chlorine? Well, ozone has some other positive aspects we should consider, too.
The Look, the Feel
Back to pool chemistry basics for a moment to illustrate what’s coming next. When chlorine enters the water (whether it comes in the form of liquid, tabs, granular, gas or even from a salt water chlorine generator), it turns into a hypochlorite ion or hypochlorous acid. The proportion of these two compounds is determined chiefly by the pH of the water. We want more of the killing form of “chlorine,” the hypochlorous acid, and more of that stuff is formed at lower pH levels.
Now when the hypochlorous acids come into contact with certain organic type stuff in the water — sweat, makeup, urine (yikes!), sunscreen, body oils — compounds called chloramines are formed. These have a strong chlorine smell and can be irritating to swimmers (in fact, they’re one of the causes of “red eye”). Sometimes called “combined chlorine,” these are not desirable forms of chlorine. They’re comparatively weak sanitizers and oxidizers, not to mention the discomfort they cause.
Normally, if you have a strong chlorine smell, or say, a foamy spa, there are chloramines present. To get rid of them, you need to add more chlorine. This seems to run against common sense, but it’s true. It is part of a complicated subject called breakpoint chlorination, but just to keep things simple, we’ll just say that the additional chlorine eats up the combined chlorine. Nitrogen and chlorine and stuff then just gas off, leaving behind cleaner fresher water.
Yeah, fascinating and all, Poolnerd, but where does ozone come in?
Since ozone is such a powerful oxidizer, any chloramines present are quickly oxidized. None are left in the pool water to bother folks. That’s good for everyone taking a swim in your pool.
Now, some rare people are truly intolerant of chlorine and alternatives like bromine. Usually it’s the combined form of these chemicals that bother them. So ozone might be a good fit for these unfortunate souls. In fact, I’ve got a job under construction right now where the woman has an extreme sensitivity to chlorine. We’re going to try ozone and very low levels of chlorine residuals, maybe even in conjunction with silver and copper ions which keep bacteria and algae, respectively, at bay. Perhaps I’ll post some updates and results on this client and her pool in a few months.
Anyway, if we’ve got a pool that’s chiefly protected by ozone, augmented with a bit of chlorine, we’ve got something real good going on. We’ve got low levels of chlorine, which is good for people, bathing suits and so on. But wait — there’s more! None of those irritating chloramines present, either. Double-plus good.
One other thing that I’ve noticed, too. Ozonated pools have a clearer, more sparkling look to them. I was skeptical when those slimy sales reps told me that. But, I must grudgingly admit, it does seem to be true. Not a huge difference, but it is noticeable.
The Next Fad in the Pool Business?
So, all in all, ozone seems to be a wonderful thing to treat pool water with. Others think so, too. For example, it’s been used to treat the water in every Olympic pool since 1984. Elite competitive swimmers say that their times are slightly faster in ozone pools. I can’t vouch for that, though — I’m nowhere close to that level when it comes to swimming.
But let’s not start thinking that ozone will be the next big thing that’ll make pools maintenance-free for homeowners. It won’t. You’ll still need to test your water on a regular basis, as well as the other stuff you should be doing (brushing the plaster, emptying strainer baskets, and so on). You’ll probably buy and add fewer chemicals to your pool, which is kind of nice. But it does has some more attractive attributes: dramatically lower levels of chlorine; complete absence of chloramines; and brighter, crisper looking water. I’ll keep trying it out on more of my projects and keep you updated.
Anyone that has used ozone on their pool(s), or that may be interested, please leave comments.
Here are some manufacturer websites to check out:
DEL Ozone
Prozone
UltraPure
February 18th, 2007 at 11:09 am
Love your web site, Pool Nerd!
Question about SWG: will they work with ozone, using them both together? Ozone sounds like something to check out for sure and I’ve heard a lot about SWG. I’m trying to get away from messing with our new (6 mos.) pool, and from what a coworker says, it sounds like this may be the way to go. Ozone and chlorine added automagically. I can spend more time enjoying the pool and sun worshipping instead, instead of doing chemicals and things.
February 18th, 2007 at 11:37 am
Barb
Thanks for the good word about the blog.
One thing first — SWG stands for Salt Water Generator, for those not familiar with the acronym.
It’s a piece of equipment that converts salt in the pool water into chlorine. Add a whole bunch of salt to the pool, install one of these miniature chlorine factories, and no more need to add chlorine.
At least that’s what the sales people tell you. They’ll also tell you it’s a “friendlier” form of chlorine; that there’ll be no more need to add chemicals to your water; that you won’t have to buy or transport chemicals again; and so on.
In the real world, though, many of those claims don’t stand up. I think that these units appeal to you and others because they believe that they’ll them save time and/or money. It will do neither.
You will still need to regularly test your chemicals, as you would for a regular pool, adding chlorine occasionally (especially in cooler weather) and acid a lot (these salt cells tend to raise pH a pretty fair amount, so need to acid to bring pH back down). Plus you’ll need to clean the salt cell itself …
Neither will they save you money. Setting aside the cost of the unit initially, in the future you’ll need to replace the cell every four or five years. Those cost about $600, which if spread out over 4-5 years is just slightly less than you’d spend on chlorine.
And there sometimes problems with corrosion, damage to deck/coping/landscaping due to salt, and other problems (check link on home page to poolbiz, a site that is critical of salt cells and salt pools).
Anyway, the downside to salt seems too great, besides being WAY oversold by sales reps. That’s the reason I’ve been trying out ozone: salt leaves a lot to be desired, and people still want low-fuss pools. Now, ozone ain’t magic, make no mistake; you’re still going to need to take care of your pool. But it does have some definite positives. Hopefully, as time goes by I’ll see more results from the pools I’ve installed it on.
Hope this helps. Enjoy your swimming and sun worshiping.
February 19th, 2007 at 5:22 am
My brother has a salt pool, too, and his salt generator is installed after the filter and the heater. He says this so the chlorine from the generator won’t go thru them, which can damage them. Do you have to do this with ozone, too? Will ozone rust a stainless steel filter tank?
My 5 year old daughter gets little itchy, rash-like bumps, which we think might be from chlorine, so we’ve been looking at using other things instead. Maybe salt isn’t so good, but ozone sounds promising. Which brand of ozone would you recommend?
February 19th, 2007 at 7:00 pm
Yes the ozonator should be installed downstream of all other pool equipment. If it is, then ozone won’t be going through the filter; and since there is no ozone residual, none will be drawn through the skimmer and therefore not into the filter. That said, perhaps it’s not a bad idea to use non-metallic filter tanks until we know more about how these chems and components interact.
About your daughter and her rash — I don’t feel qualified to address that. My first thought was that it’s more likely chloramines than chlorine, but it may be something else entirely. Have you had your family physician look at it?
I don’t feel real comfortable recommending any particular brand. The manufacturer I use makes a product suited to my needs; your needs may be different, so I’d hate to tell you to get brand X when Y may be more appropriate. Please just consider this post a starting place, then do a little more research on your own. Check with the local pool store, pool service people, coworkers, friends and family, maybe an online forum.
Boy, looking through this response to your questions, I wasn’t a whole lot of help, huh? If, after checking into things a bit more, you still have questions, please email me.
March 13th, 2007 at 10:42 am
Yes, ozone is the best answer that we have found. We do put an errosion feeder on the system for residual, but we keep the chlorine count down around .6 to .7 Just enough to cover when the ozonator is off. We have used both types CD and UV and have found the UV more reliable. Our climate is moist which has some negative effects on the CD units by way of nitric acid in the lines. The newer units from Dell have corrected that to a degree, but the UV units are very trouble free. As for the volume of O3, since most units “over produce” it is hard to say what the difference is between a lot too much or a little too much. As long as the pool has available all that it can inject, what difference does it really make? The best part of UV is that it cost so much less per unit. We put them on every pool and haven’t regretted it for a minute. It makes the pool much easier to maintain for the customer (a lot higher margin for error when they forget to add something). It has worked for years on spas for us, applying to pools has been equally pleasant. I don’t think brand is as important as installation method. Venturi is the only way to go with a bypass valve to control flow through the venturi (don’t want the bubbles to make noise in the pipes). We avoid the problem of air in the chlorinator or the chlorine hurting the components of the ozone by using a Pentair Rainbow 300 off-line. We pick up the water right at the pump output and return it to the last pipe heading back to the pool after the ozone. Works perfect.