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Chloramines: The Culprit Behind That Familiar “Pool Smell”

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If you’ve been around pools long enough, chances are you’ve come across one or two that had a pungent, chlorine pool smell.

While it may seem like they were overloaded with chlorine, what they were actually overloaded with are chloramines.

At high levels, chloramines are extremely unpleasant, and can irritate your nasal passages, lungs, eyes, skin, and even affect your taste. 

What Is Chloramine? 

Chloramine (also called combined chlorine), is the gaseous by-product that results from the mixing of ammonia with free chlorine.

Swimmers pollute pools with ammonia. It’s in their sweat, sunscreen, and yes, even urine (don’t pee in the pool, people!). This is why public pools require you shower before going in.

Chlorine can only sanitize so much. Technically, it’s always oxidizing to prevent chloramines from building up. But, after a certain point there’s not enough chlorine left to do the job.

If a pool’s giving off a very strong chlorine smell (ie. public indoor pools), it’s pretty much a given that the water is heavily polluted. 

Why Chloramines Make Your Pool Smell (And Worse)

Chlorine sanitizes water by releasing two chemicals: hypochlorous acid and hypochlorite ion. The measure of the chlorine in these is referred to as free available chlorine (FAC).

FAC is reduced when it reacts to ammonia contaminants (sweat, sunscreen, pee), forming chloramines (aka combined chlorine).

Looking at the chemistry behind it, there are 3 potential chemical reactions that can occur when hypochlorous acid reacts to ammonia.

These reactions replace ammonia’s hydrogen ions with chlorine ions to form either: 

  • monochloramine (a single ion replacement)
  • dichloramine (2 replaced ions)
  • trichloramine (3 replaced ions)

Monochloramine is the safest of the three, and can be used as a disinfectant. In fact, monochloramine is sometimes added to drinking water to purify it.

However, dichloramine and trichloramine are the ones you need to look out for. They both cause water to have that pungent, chlorine smell, and they can wreak havoc on your health, irritating your skin, eyes, and lungs.

If exposed to them over long periods of time, some people (ie. lifeguards) can develop chloramine sensitivities at even the lowest levels. When this happens it usually means you can no longer be around pools.

How to Test Chloramine Levels

A well-maintained pool should actually have no smell to it, so if it’s emitting a very strong chlorine odor, you know it’s time to test for combined chlorine (chloramine) levels.

The upside is that test strips or liquid test kits are widely available for testing chlorine levels. The downside is you’ll have to do a bit of math as most kits only test for free available chlorine (FAC) and total chlorine (TC).

So how do you find out the combined chlorine level in the pool?

First, understand that combined chlorine should be less than 0.2 parts per million (ppm). 

Next, you’ll have to figure out the free available chlorine and total chlorine levels. The FAC level should hover between 1.0 and 4.0 ppm for chlorine to stay effective, never dipping under 1.0.

By testing the pool water with test strips or a liquid kit, you can get fast and accurate readings.

Test strips require you to take a sample of the pool’s water and dip the strip in it. You then match up the colors on the strip with the chart on the back of the bottle which provides the readings.

Liquid test kits include an apparatus for the water sample, as well as chemicals to add into the water sample. You then match the resulting water color against the provided chart.

For chlorine testing, the equation you’ll want to remember is:

FAC (free available chlorine) + CC (combined chlorine) = TC (total chlorine)

As these kits only test for FAC and TC, you can determine the level of chloramines in the water using this equation:

TC – FAC = CC

How to Prevent Chloramine Buildup

It’s very important to keep chloramines from building up and overwhelming swimmers with their powerful scent and dangerous attributes.

Keep Your Chemistry Balanced

Pool water chemistry is a delicate beast, and the pH level is what needs to stay balanced so you don’t end up with water issues.

Too low of a pH level, your water becomes acidic. Too high, alkaline.

Keeping the pH level balanced requires you to frequently test the water (moreso if it’s a public pool), as various contaminants can enter the water and throw the balance off.

This can be the result of pool water features changing the water’s temperature, fluctuations in the outside temperature, airborne contaminants landing in the pool, or swimmers themselves.

The pool’s water is made up of a myriad of chemicals that keep the water clean: things like chlorine or bromine, as well as stabilizing agents and various other chemicals.

By keeping this chemistry balanced, you’ll avoid chlorine levels becoming so depleted that chloramines are created.

Keep Your Pool Well Ventilated

Chloramines are a gaseous compound that’s inhaled or absorbed through the skin. It does not react well with the human body, and causes irritation that can lead to serious health problems.

Keeping your pool well ventilated is going to be paramount in protecting people from inhaling chloramines if they’re present in the pool. This is because chloramine gas is heavier than air, allowing it to sit on the surface of the pool. 

Imagine every time you come up for air and you’re inhaling a deep breath of chloramines.

Not too pretty.

So, indoor pools have a very real challenge in staying well-ventilated to keep air flowing and driving chloramines from the surface. Obviously, outdoor pools are wide open, so the ventilation issue with them is non-existent.

Encourage Proper Pool Etiquette

Any time you (or anyone else for that matter) wants to go for a dip, you should always shower before and after.

Why before? 

The ammonia from your skin’s sweat will break down the pool’s free chlorine, and if there’s already a low chlorine level, chloramines will be born. 

Skin that has sunscreen on it is another common offender, as is urine (please note: not peeing in the pool is about as proper as you can get when it comes to pool etiquette).

Why after?

If the pool is riddled with chloramines, you don’t want to let them (or any other harsh chemicals for that matter) linger on your body. They can be absorbed through the skin or inhaled until you clean yourself off. 

How to Remove Chloramines

When we talk about removing chloramines and that awful pool smell, what we’re really doing is returning the pool water to a balanced state, effectively neutralizing the chloramines.

Use Pool Shock (More Chlorine)

Shocking the pool is the easiest and quickest method to get rid of chloramine levels. 

What’s happening when you add pool shock is you’re spiking the water’s chlorine levels to not only sanitize it, but also oxidize the chloramines. Shock treatment boosts the FAC level of the pool, and also kills any bacteria in it.

This can be done every few weeks to keep things in check, and some owners will even shock once a week if the pool is under heavy use.

Use Non-Chlorine Shock (Oxidizer)

While pool shock acts as a super chlorinator, non-chlorine shock is an oxidizer. 

By adding MPS (monopersulfate) to the water, it oxidizes the chloramines, allowing the free chlorine in the pool to separately attack bacteria and algae.

Non-chlorine shock is a great alternative to chlorinated pool shock as you don’t have to wait hours to use the pool after applying it. But if there’s the need for increased FAC levels, or there’s been an “accident” in the pool, you’ll need to use traditional chlorinated shock.

Use A Secondary Sanitizer (UV / Ozone)

A secondary sanitizer like a pool ozonator is another option to filter out chloramines. 

Pool ozonators create ozone gas via high voltage ionization process or UV radiation treatment. 

Compared to chlorine, ozone is about 100 times stronger as an oxidizer, which will keep the pool water clean. 

One of the main benefits of using a pool ozonator is that they don’t affect your pool’s pH level, which means less chemical adjustments to your chlorine or salt water pool.

Uhm… Was That You?

So now you know what chloramines are, and how they’re the cause of that god awful pool smell that you’ve come across at some point.

While they’re not exactly harmless, the good news is that they’re relatively easy to keep controlled as long as you understand how to keep your pool’s water balanced.

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