Aquatic Technology Pool & Spa

Chlorine Conversations

Chlorine Conversations

By Paolo Benedetti

In recent years, it’s been difficult to avoid two large and related discussions about water treatment as it relates to swimming pools and spas.

One the one hand are discussions of the evils of chlorine, which, after more than a century of common and beneficial use, is still widely misunderstood by homeowners and many professionals in the watershaping trades. On the other are conversations about chlorine-free pools and spas – another set of exchanges where there’s proving to be lots of room for misunderstanding and more than a little confusion.

Those may seem to be flip sides of the same controversial coin, but they’ve actually managed to stay fairly separate. That’s why, in this article, I’ll deal with them one after another, first doing what I can to set the record straight about chlorine and defining what more people need to know about what it is and how it works, then exploring what’s involved in leaving it out of watershapes meant for human immersion and recreation.


It may just be promotional hooey put forward by those who want watershapers (and their clients) to seek alternatives to chlorine as a water sanitizer, but by now we’ve all heard about the perils of chlorine: burning eyes, itchy skin, green hair and that dreaded “smell of chlorine” around a watershape.

The plain and simple truth is that chorine is not the cause of these concerns: What people are mostly experiencing is actually waste products of the sanitizing process that accumulate in the water when there is not enough chlorine available in the pool or spa to destroy them.


Again, plain and simple: The problems commonly associated with chlorine almost always are the result of other water chemistry issues generally traceable to improper chemical maintenance, testing and dosing. Itchy skin, for example, is attributable to insufficient chlorine in the water; green hair to excess copper in the water; and burning eyes to improper pH or an inadequate chlorine concentration, either of which results in formation of eye-irritating ammonia compounds.

For all that, a great many people (professionals among them) immediately point a finger at chlorine, mainly because they smell what they assume is chlorine. In actuality, what their noses detect are ammonia compounds and gasses: These malodorous substances form when chlorine combines with bather waste and the water starts to smell like chlorine bleach. The instant and overly easy assumption? There must be too much chlorine in the water!

That’s incorrect. What they’re really smelling is actually a lack of chlorine and the dominance of ammonia compounds in the form of chloramines. When there is a sufficient quantity of chlorine in the water, chloramines cannot form. When bather load exceeds the quantity or feed rate of chlorine, chloramines gain a foothold.

This is why a bather “smells chlorine” on his or her skin after swimming, when in fact that odor is perspiration combined with chlorine. A simple shower with soap and water will remove the offending fragrance.


Years of public misperception of these facts of chlorine performance have led various suppliers and professionals in the watershaping industry to seek out and promote “chlorine-free” pool options.

Salt water pools are part of this phenomenon: Suddenly, everyone was talking about this approach to water maintenance – and just as suddenly, these systems were being promoted as a “chemical-free” alternative to standard chlorine approaches.

But these salt systems are not chemical-free! True, homeowners and technicians no longer carry and add chlorine directly to the water, but the reason this is possible is because a salt system manufactures its own chlorine in the water by separating the sodium and chlorine in common salt. Not dumping a powdered or liquid form of chlorine into such a pool does not mean it is not there!

Through the years, there have been times when other approaches have stepped under the “chlorine-free” umbrella – ozone generators, ultraviolet systems and metal ionizers among them. Ozone in particular is promising, because it has thousands of times the oxidizing power of chlorine and the other halogens (including bromine and hydrogen peroxide) most frequently used in water treatment.

The thing about these systems is that the work best in partnership with chlorine, with the ozonator, UV system or ionizer taking on the bulk of the oxidizing or sanitizing while chlorine stays in the water as a residual sanitizer, so there’s something on hand to keep contaminants at bay when the main system isn’t in operation.

That’s the big reason why it’s been so difficult to move away from chlorine in watershape systems: Without chlorine’s staying power – its ability to do its job 24 hours a day, seven days a week – those other systems need to operate 24/7 to get the job done. And if they’re operating all the time, the cost of water maintenance goes up significantly.

What this all boils down to is a big point about chlorine: There’s nothing wrong with it! This substance has been used for more than a century and is so safe and time-tested that it’s used to protect drinking water almost everywhere around the globe. Even to this day, it is used in almost every commercial swimming pool there is to maintain clear, safe and sanitized water.


Those who would step away from chlorine and are bent on denying its safety have become quite good at spreading misinformation about it. Granted, there are some unlucky people who are particularly sensitive to chlorine and react negatively when they swim in pools in which it is used, but by and large (and not to understate the potential for negative experiences among those who can’t tolerate exposure to chlorine), the anti-chlorine advocates overstate the case to make their points.

As mentioned above, for example, chlorine does not turn hair green, but the presence of copper in the water as a result of improper pH maintenance certainly does: When the blue staining agents in copper come in contact with blond hair, blue plus yellow makes green.

When a pool is overdosed with chlorine at, say, three to five times the recommended level, there’s no “chlorine smell” at all because there are no chloramines to generate the odor. And when chlorine is used at correct levels, there is no burning sensation in the eyes either – but there certainly will be if the pH is out of line or there are chloramines present.

In fact, most people who are sensitive to chorine – including those with asthma – are actually having a negative response to chloramines: These substances are the real villains in the chlorine story.

On the positive side, chlorine eliminates countless biological contaminants from the water safely and efficiently, including (but not limited to) Staphylococcus aureus, Cryptosporidium, E. coli, Legionella pneumophila and a range of human pathogens carried in blood, saliva, feces, urine, perspiration and mucus.

None of this has prevented those with an interest in promoting chlorine alternatives from digging deep to undermine this genuinely helpful substance. Yes, chlorine is a carcinogen, but when you look closely at the studies saying so, you notice that the exposure must be prolonged and that the concentrations are far higher than anyone would ever encounter, even in a horribly mismanaged watershape.

On that extreme level, water itself is suspect. Did you know, for example, that if you drink too much water in too short a time, you can kill yourself via a weird form of drowning? The key for both chlorine and water is moderation. And for chlorine, the golden path, the grand revelation, is the use of even, consistent micro-dosing.

With some of our commercial projects, for instance, we’ll cart barrels of liquid chlorine and set them up with metered dosing systems that deliver small, steady quantities to the water. In big competition pools, we’ll set up on-site electrolytic systems that produce chlorine on site.

In these cases, we set up control systems to track oxidation-reduction potential (ORP) and pH: These units automatically and instantaneously respond to the demand for additional (or fewer) chemicals – adjustments necessitated by changing bather loads, for example, or by temperature fluctuations.


If you combine one of these sophisticated monitoring systems with a metered chlorine supply and, say, an ozone generator, you end up with a watershape that is about as “chemical-free” as humanly possible. But, strictly speaking, close to chemical-free is still not really chemical-free – and so the quest continues.

But the fact of the matter is that these pristine, chlorine-free pools and spas are within reach – although they come at a cost, at least so far as the possibilities now under discussion go.

Let’s back up a bit and consider the nature of the chlorine- or chemical-free challenge: For the water to be truly safe for human contact and immersion, such a system needs to include a sanitizer – that is, something to kill germs and bacteria. To be effective, this sanitizer must be present and available in the water 24 hours a day, every day. In addition to this residual, the sanitizer must also be ready for injection to handle spikes in temperatures and in bather loads.

The system also needs to include an algaecide. The most effective of these agents are metal ions including nickel, copper and silver. In microscopic doses, they work well and are safe for the environment, but the truth is that there is no easy way to measure their levels in a typical pool/spa system, so unusual care must be used in setting things up.

There are several ways to get metal ions into the water. Pouring a metal-containing algaecide into the pool is one approach, but this violates the spirit of the chemical-free approach and can easily result in excessive dosing. Erosion ionizers are an option here: These cartridges or balls contain metal compounds that are released into the water as it circulates past or through them. There are also ionizers that use electricity to emit metal ions into the circulation system.

Contrary to manufacturer's claims, however, metal ions do very little to kill bacteria and germs. Instead, they work gradually to keep algae and plant life at bay.

As for sanitizing, ultraviolet light is an increasingly popular option. As water circulates past an enclosed, UV-emitting lamp on the equipment pad, the high-energy light destroys germs and bacteria before the water is returned to the pool or spa.

Ozone generators are even more effective as sanitizers. Not only do they destroy germs and bacteria, but they’re also effective in breaking down contaminants that work their ways into water, including fabric softeners, cosmetics, suntan lotions, soap and shampoo residues. These units work by generating ozone gas that is injected directly into the water. The gas is hugely reactive and stays in its active form for only a brief time.

Both of these systems – UV and ozone – sanitize the water only when turned on and operating: Cut off the power and, within seconds, the sanitizing action stops. There is no active residual.


To achieve a truly chlorine-free pool thus requires that the available non-chlorine systems – ultraviolet or ozone – be in operation at all times. Operating a properly sized ozone system 24 hours a day is expensive, however, so that is less than desirable. As an alternative, an ozone system can be used in tandem with a UV unit, with the ozone system on during peak bathing hours for maximum oxidizing capacity and the UV system covering the sanitizing during the rest of the day. But even so, such a combined system is likely to be too costly for most applications – and this is why so many of them operate alongside dosing systems that add small, steady amounts of chlorine to the water.

Another Possibility

In this discussion, I have completely set aside any consideration of natural swimming pools – that is, those watershapes that use plants and biological filtration to keep the water clean and clear.

The operating dynamics of these systems are so distinct from those of conventional pools and spas that I see their chemistry as a completely separate topic – one worthy of detailed discussion, but not in this article.

-- P.B.

My friend Randy Beard (Pure Water Pools, Costa Mesa, Calif.) wrote not long ago about a system in which he uses a UV unit in conjunction with a highly efficient variable-frequency-drive pump to run his client’s watershapes 24 hours a day (click here). He also draws off a certain amount of water to irrigate the landscape, using fresh fill to keep the pool’s water at a drinkable level. Nonetheless, he acknowledges that he uses chlorine occasionally to keep up with spikes in bather load and high temperatures.

This is where I come down in these discussions: Like Randy and others, I improvise with systems based on my understanding of bather loads and temperature trends and combine a strong sanitizer (ozone, UV light or both) that runs for six to eight hours a day with a feed system that adds tiny amounts of chlorine to maintain a residual in the vicinity of 0.5 parts per million for the remaining hours of the day.

These systems aren’t chlorine-free, so to speak, but I describe them as “ultra-low chlorine” pools. And again, this comes at a cost: To maintain chlorine at that low a concentration, the system needs to be equipped with an ORP/pH monitoring system that will micro-dose the chlorine as needed. These systems aren’t inexpensive to start with, and as functional components they add to the cost of energy associated with their watershapes.

At 0.5 ppm, the water in a pool has about as much chlorine in it as the drinking water most of us experience in our daily lives – safe for human consumption and, if you follow Randy Beard’s lead, safe for watering plants.