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Understanding Chlorine

Chlorine. It’s the chemical everyone loves to hate. However, much of the disdain for chlorine comes from some key misunderstandings about chlorine and it’s attributes. There is a reason that chlorine has been used to sanitize pools since 1908. It is highly effective at sanitizing and when used properly it does NOT cause itching skin, red eyes, or have that “chemical smell” that most people ascribe to it. For many years, efforts have been made to come up with an alternative to chlorine. Bromine, Bacquacil, ozone, UV, and now salt systems just to name a few. Ultimately the claims of these sanitizers as being an “alternative” to chlorine are misleading and just an attempt to market a product. When it comes to sanitizing a pool, it always comes back around to chlorine.

Some facts about chlorine alternatives:

  • Bromine – For many years bromine was marketed as an alternative to chlorine.  The misleading thing was that all bromine sold until a few years ago contained a significant percentage of chlorine as it’s chemical makeup.  Additionally, unlike many forms of pure chlorine, bromine is not stabilized against burning off from the sun and costs about double what chlorine does.  As a result of being un-stabilized and it’s unit cost, bromine pools cost about 4x as much as chlorine pools and yet still contain chlorine!

  • Bacquacil – Another alternative to chlorine that was big in the 90’s, Bacquacil claimed to be gentler on the skin than chlorine.  However, the active ingredient of Bacquacil is hydrogen peroxide, which is irritating on the skin in it’s own right.  Additionally, Bacquacil is plagued with issues such as its incompatibility with certain types of filters and the “Bacquicil Wall”, in which pools reach a point (typically after about 3 years) where they will always remain cloudy.

  • Ozone – Ozone is a great oxidizer, however its lifespan is extremely short-lived.  It is a great supplemental oxidizer in small bodies of water like hot tubs, but is not effective in treating large volumes like swimming pools.  Ozone systems ARE used effectively in Europe where they have separate tanks where pool water is circulated away from the pool and treated directly with ozone in small batches.  American swimming pools are not designed for this method and therefore ozone is not useful in treating pools here for that reason.


  • UltraViolet – Just like ozone, UV is an effective oxidizer, but it must be used in conjunction with chlorine.  Additionally, effective UV systems are very expensive.

  • Salt Systems – Salt systems are the latest method of pool sanitation and offer tangible benefits for pool owners.  However, salt systems are simply a new way of delivering chlorine to a pool (hence their alternative name, “chlorine generators”).  Salt systems have been marketed extensively as “alternatives” to chlorine, but the salt is just a vehicle for delivering plain old chlorine to a pool.  Check out our Salt Systems page for more details.

All of these chlorine “alternatives” either must be used in conjunction with chlorine, contain chlorine, or do not perform very well as a sanitizer!

So, why the bad rap?  What is it about chlorine that makes people want to look for an alternative sanitizer for their pool?  Every one of us has had the experience of walking into the YMCA or the hotel pool and smelling that “CHLORINE SMELL”… right?  Or gone swimming at a friend’s pool and gotten out with itching skin or red eyes, reeking of "chlorine".  Everyone seems to have had a bad “chlorine” experience at some point.  Well, the reality is, that none of those things are due to chlorine.  They are due to a byproduct of chlorine and pool operators not understanding how chlorine works.  A properly maintained chlorine pool will NOT smell like “chlorine” and will not cause skin or eye irritation!

Chlorine vs. Chloramines Explained

(This is a little complicated, but if you stick with us we promise it will make sense!)

  • When chlorine is added to a pool (regardless of the form; tablet, powder, liquid, granular, gas, or via chlorine generator [aka salt system]) it is called FREE chlorine.  It is “free” and available to do it’s job and attack a contaminent (dirt, bacteria, algae, etc.).

  • Once the chlorine finds a contaminant the “free” molecule of chlorine combines with the contaminant and forms something called “combined” chlorine (also known as a CHLORAMINE).  The combined chlorine is used up chlorine.  It is no longer serving any beneficial role in the pool.

  • In order to eliminate the combined chlorine a SECOND particle of free chlorine is necessary to combine WITH the combined chlorine.  When that happens an oxidation reaction takes place, a gas is given off and it is eliminated from the pool.

  • So, if there are 2 particles of chlorine in the pool for every particle of contaminant, the pool will never have a problem.  The free molecule of chlorine combines with the contaminant, a second free molecule combines with that, it oxides, gases off and the process continues over and over again without any issues.

  • Problems arise if there is ONLY enough free chlorine to create combined chlorine, but not enough extra free chlorine to get RID of the combined chlorine once it is created.  The typical scenario is that the free chlorine level in the pool is allowed to get down to zero for a period of time and the combined chlorine (aka CHLORAMINES) become established in the pool.

  • Chloramines cause cloudy water, itchy skin, red eyes, and the SMELL OF “CHLORINE”.  This is where people get confused.  Because they smell “chlorine” they assume that the chlorine is too HIGH in the pool and stop adding more.  This is the opposite of what needs to happen.  The pool smells of “chlorine” because there are chloramines that require MORE FREE CHLORINE to be added!

  • Once chloramines have become established in an environment with no free chlorine for a period of 24 hours or more they become VERY resilient.  At this point a normal amount of free chlorine will no longer get rid of the combined chlorine.

  • If chloramines have become established the pool now needs to reach what is called “Breakpoint Chlorination” in order to get rid of them.  Breakpoint Chlorination is the addition of TEN TIMES the amount of combined chlorine in new, free chlorine to get rid of the established chlorine.  This is a LOT of chlorine.  Adding a regular amount of chlorine will no longer get rid of the chloramines.  The precise breakpoint needs to be REACHED OR EXCEEDED in order to get rid of the chloramines.

  • Since the person maintaining the pool didn’t understand what happened chemically to create this problem they don’t understand what the issue is or that breakpoint chlorination needs to be reached.  Consequently, many residential, hotel, motel, and apartment pools constantly operate in a condition where chloramines are present.

  • Since many (maybe even most) pools are plagued by this underlying issue with chloramines, most people associate itching skin, red eyes, and the smell of “chlorine” with swimming in a chlorine pool, when really it is due to the chloramines (and the original LACK of chlorine) that caused the problem.

  • A pool that always has enough free chlorine will never have these issues.  This is why salt systems have gotten such rave reviews.  A salt system is a chlorine generator.  Since it is constantly generating chlorine it never allows the pool to exist in a zero-free-chlorine state long enough to create a problem with chloramines.  A pool with a traditional chlorine feeder that is always stocked (about once a week) will also NOT have a problem with chloramines!

  • A pool that develops a chloramine problem that is properly “shocked” to reach or exceed breakpoint chlorination will also successfully resolve any issues that were created.



So, now you know more than you ever wanted to about chlorine, but hopefully have a better understanding of how it works.  Used correctly, via either a chlorine generator (salt system) or with a properly stocked chlorine feeder, chlorine is a great sanitizer.  Avoiding the common pitfalls of its use will allow you to have an enjoyable pool, free from the problems caused by chloramines.  

The descriptions and wording contained on this webpage are exclusively the property of Bryan Mills / Atlantis Pool Service LLC.  Any reproduction or use without the consent of Atlantis Pool Service is strictly prohibited.

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