Does your pool have a strong chlorine smell?
This is a common problem with chlorine-based swimming pools, and it happens even when you don’t have a high level of chlorine to justify it. Fortunately, it’s not something you have to tolerate.
We’re going to cover why this funky smell occurs, how to go about fixing it using two different methods, and how to prevent it going forward.
Quicker answer: It’s caused by chlorine reacting with nasty stuff in your water. When chlorine combines with certain contaminants, it forms chloramines, and a high level of chloramines creates a pungent “chlorine smell”.
Does Chlorine Have a Smell?
Chlorine has a subtle smell before it’s added to your pool, but this is NOT the same as the strong “chlorine smell” you’re likely experiencing.
If that surprises you, consider that when adding chlorine to your pool, you don’t get the same nasty chlorine smell you experience until you’ve added it to your water. Even then, the smell comes much later on.
This is because it’s not the chlorine itself that smells, but the byproduct of a reaction that happens in your water.
Let’s explain…
Why Does Chlorine Make Your Pool Smell Bad?
If chlorine doesn’t really have a smell, why does it make your pool smell?
Here’s why:
When you add chlorine to your pool, it immediately starts neutralizing contaminants in your water.
Chlorine targets things like algae, insects, dust, dirt, rain, animal waste, bather waste, beauty products/toiletries, and any other contamination that manages to find its way into your swimming pool.
Now, some of this nasty stuff, especially human sweat, saliva, and urine, for example, combines with your free chlorine to form a new compound called combined chlorine, also known as chloramines.
When enough of these chloramines are able to build up in your water (over 0.5 parts per million is considered a problem), they give off a strong odor that many people mistake as a high concentration of chlorine.
In short, it’s a high concentration of combined chlorine (chloramines) that are responsible for that familiar pool chlorine smell — not chlorine.
How Do You Fix the Chlorine Smell in a Pool?
To get rid of the chlorine smell in your pool, you simply need to deal with the buildup of chloramines in the water.
You do this by shocking the water.
Shocking your pool breaks chloramines apart, in turn reverting them back to their basic elements. This process is known as “oxidation” and it effectively removes the chloramines from your pool.
There are two main types of shock treatment you can use in your pool, each with its own benefits and drawbacks.
Let’s walk you through both options:
Option #1. Use Chlorine Shock
You don’t need any fancy new chemicals for this. By far the most popular way to oxidize and get rid of chloramines is to just use regular chlorine.
Liquid chlorine is an ideal shock treatment as it’s one of the purest forms, though granular chlorine (usually dichlor or calcium hypochlorite) will get the job done at the cost of adding lots of cyanuric acid or calcium to your water.
Chlorine tablets (usually trichlor-based) aren’t suitable for pool shocking as they dissolve too slowly in the water.
Using this approach, you’ll need to add enough chlorine to get your chlorine level to at least 10 parts per million, though your target shock level could be much higher if your stabilizer (cyanuric acid) level is also high.
Pros:
- Very effective at oxidizing chloramines
- Very effective at killing all types of algae
- Easy to source chlorine-based shock locally
- Generally cheaper than other types of shock
- Can be used in both indoor and outdoor pools
- Liquid shock doesn’t add unnecessary chemicals
Cons:
- Temporarily increases chlorine to unsafe levels
- Dichlor shocks add lots of cyanuric acid to your water
- Cal-hypo shocks add lots of calcium to your water
Note: We have a full guide on how to shock your pool using chlorine. This will walk you step-by-step through the process.
Option #2: Use Non-Chlorine Shock
Non-chlorine shock also goes by the name “Potassium Monopersulfate”, or “MPS” for short.
Unlike chlorine, non-chlorine shock is only an oxidizer; it doesn’t double up as a sanitizer or disinfectant.
While it can be used to oxidize and remove chloramines in your water, it does so at a much slower rate than chlorine-based shock, which means it’s not as suitable for dealing with higher levels of combined chlorine.
Instead, non-chlorine is better at oxidizing contaminants before chlorine gets involved, helping to prevent more combined chlorine from forming in the water. In that sense, it’s far better as a preventative than a solution.
Pros:
- Doesn’t raise the chlorine level in your water
- Allows for quicker use of the pool after shocking
- Assists chlorine in dealing with contaminants
- Doesn’t raise calcium or cyanuric acid levels
- Less harsh on pool surfaces and equipment
- Can be used in both indoor and outdoor pools
Cons:
- Slow at oxidizing chloramines
- Can cause misleading chlorine readings
- Not effective against algae
- Generally more expensive
How Often Do You Need to Shock?
Shocking your pool is usually a weekly or twice-weekly task, especially during the summer months when your pool gets the most use.
However, you can also shock your pool as needed. For example, if someone has a little accident in the water, a wild animal dies in your pool, or, of course, if your pool develops a strong chlorine smell.
It’s worth noting all of these factors ultimately lead to a high level of combined chlorine, which shocking your pool is designed to alleviate.
This is why regularly testing your combined chlorine level (along with the rest of your water chemistry) is the most reliable way to know when to shock. If you see a reading above 0.5 for combined chlorine, it’s probably time to shock.
How Do You Prevent the Smell from Coming Back?
While shocking your pool regularly is the best way to prevent a chlorine-smelling pool, it’s not the only thing you can do.
Fortunately, most of these preventative measures are just part of good pool maintenance, so you’ll just need to tighten up the basics.
Specifically, you’ll want to:
Keep your water balanced. A balanced pH level between 7.2 and 7.8 will allow your chlorine to work better, helping it neutralize and oxidize contaminants before they have a chance to form into chloramines.
Maintain a high enough sanitizer level. Similar to the point above, when your chlorine level is too low for too long, it won’t have enough “power” to oxidize contaminants, thus allowing chloramines to build up in the water.
Encourage swimmers to shower. Showering before entering the pool decreases the number of chloramines formed from excess sweat, lotions, and other swimmer-derived substances.
Use a pool cover. A cover will reduce contamination and reduce the load on your chlorine. As above, fewer contaminants mean less organic matter for chlorine to react with, which decreases chloramine formation.
Keep your pool well-ventilated. Proper ventilation allows chloramines to off-gas more easily from your water without accumulating in the air (which can be dangerous to inhale, especially in indoor pools).
Consider a secondary sanitizer. While an expensive solution, installing a UV or ozone system will help to assist chlorine with sanitizing the water, leaving more of your free chlorine to oxidize combined chlorine.
The Bottom Lime
The infamous pool smell is caused by chlorine reacting with all the nasty stuff in your water, leaving behind chloramines.
Ironically, eliminating chloramines (and the smell) is done by simply adding a lot more chlorine to your water in order to shock it. Alternatively, you can use a non-chlorine shock to assist chlorine in the oxidation process.
