Here’s Why Your Pool Water Smells Bad (And How to Fix It)

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Jumping into a crystal clear swimming pool is one of the most refreshing experiences on a hot summer day.  But, if the pool is dirty it can certainly detract from the overall experience.  

While the visual appearance of the pool water goes a long way in perception of cleanliness, its smell can also play a huge factor.  

Ideally, pools should not emit much odor at all.  Even the traditional pungent “chlorine” smell associated with pools is often indicative of potential sanitary concerns, similar to when pool water tastes bad.

Other times, pool water may smell musty or like rotten eggs –neither of these are desirable scenarios for a pool owner or its swimmers.  No one wants to exit the pool with a new stench on their body.

In this post we’ll look at reasons why pool water smells bad, and what can be done to eliminate the odors.  

Let’s hop in!

Why Does My Pool Water Smell Bad?

Pool water that smells bad can make even a clear pool appear dirty (and it likely is!).  Sometimes the smell may be faint and only apparent if you’re in the water, whereas other times the smell could occupy the surrounding yard.

The type of smell and the strength of it can both factor into the potential severity, and the action needed to remedy the situation.  These foul odors are often a result of organic decay, poor water chemistry and bacteria.

We’ll investigate a few common types of odors from pool water that swimmers may notice.

Pool Water Smells Musty

Pool water that smells musty may remind swimmers of a damp basement or crawlspace.  It emanates a moldy or stale smell, which should rightfully cause reluctance for potential swimmers to enter the water.

The musty smell is often attributed to organic build up in the water.  Organics include leaves, bugs, algae and other living matter.

While organic growth in the water may not immediately cause the musty smell, its eventual decay could.  For instance, leaves that have freshly fallen from a tree do not immediately smell stale –but, if you leave them sitting in a damp pile for a week, they may start to decompose and smell foul. 

Allowing large amounts of debris to remain in the water will eat away at your free chlorine, leaving the water less protected against other growth.  The decaying matter will also release unwanted byproducts such as phosphates into the water, which provides food for algae. 

The combination of reduced free chlorine and higher phosphates provides a favorable environment for an algae bloom.  Even though algae may not immediately cause the pool to smell musty, once it starts to break down it can cause the stench.

How to Eliminate Musty Smell from Pool

Once you’ve confirmed that the pool is the source of the musty smell, it’s important to take action.  

The first thing you should do is clean out any visible debris from the pool.  Use the pool vacuum and skimmer to remove leaves, dirt and bugs.  

After cleaning up the pool, measure the chemical balance, including free chlorine, pH and cyanuric acid.  Add an appropriate amount of chlorine to the pool to shock the water, and run the filter for 24 hours. This will kill off any remaining organic material that may be in the water. 

Pro Tip: Liquid chlorine, such as unscented bleach, is an effective pool shock.  The quantity to add will depend on pool size and the current chemical balance in the water.

Once the pool water is balanced and sanitized, the musty smell should go away.  

If the smell continues to persist, try to aerate the water to allow for off-gassing of any residual compounds in the water.  Aeration can be promoted by vigorously splashing or other means that will agitate the water, such as pointing the return jets upwards.

Finally, if you still can’t shake the musty smell, consider having the pool’s phosphate level measured.  Pool stores may perform the test, otherwise, a test kit can be purchased.

Phosphate levels higher than 500 ppb can provide a source of food for algae.  While it’s likely not a sole cause of algae outbreaks that lead to musty-smelling water, it could be a contributing factor.  A phosphate remover can be used to knock them down to a more tolerable range.

Pool Water Smells Like Rotten Eggs

The classic rotten egg smell can be one of the most offensive odors we run into.  It’s often enough to make us head in a different direction when we come across it.

In rare instances, it’s possible that pool water can smell like rotten eggs.  Most guests will steer clear of the pool if this unpleasant odor is coming from the water.

If the pool water smells like rotten eggs, it’s usually due to the presence of hydrogen sulfide gas (H2S).  Our noses can detect hydrogen sulfide in concentrations at less than 1 ppb, which indicates just how potent the compound’s smell is.

While hydrogen sulfide can be toxic in high quantities, it’s extremely unlikely that it will accumulate to dangerous levels in the pool.  

The common cause of the rotten egg smell emanating from the pool often starts with high sulfate levels in the pool.  Sulfates are naturally occurring compounds found in soil and water sources.

When filling the pool with well water, there’s a potential that sulfates may be introduced.  Generally municipal water doesn’t usually have high quantities of sulfates.

While sulfates alone don’t cause rotten egg smell in the pool, the presence of sulfur-reducing bacteria can convert them into hydrogen sulfide.  This conversion into hydrogen sulfide is what can cause a pool to smell like rotten eggs.  

Sulfur-reducing bacteria may form if the water isn’t being adequately sanitized.

How to Eliminate Rotten Egg Smell from Pool

To get rid of the rotten egg smell from your pool, it’s key to eliminate that sulfur-reducing bacteria.  Removal of the bacteria will stop the production of hydrogen sulfide in the pool water.

The quickest way to achieve this is by shocking the pool.  The elevated free chlorine will kill off any organisms in the water.

Once the water is clear of the bacteria, the pungent smell should subside.

To help further keep the rotten egg odor at bay, you can aim to reduce sulfates in the water.  This can be done by partially draining and refilling the pool with fresh water.  

When refilling, it’s important to use a source of water that has lower levels of sulfate.  If this is not practical, then it’s even more important to always keep the chlorine levels at an effective level to prevent the bacterial growth.

If using well water to fill the pool, you can send the water to a lab to measure the sulfate level.  This can help provide you with insight as to whether your fill water could be adding sulfates to the pool.

Pool Water Smells Fishy

It’s difficult to compare swimming in a pool to swimming in a pond.  Yes, they’re both bodies of water that can feel refreshing on a summer day, but that’s about where the similarities end.

Natural bodies of water are maintained through a living ecosystem, while pools are maintained through chemicals and mechanical filtration.

If the pool water smells fishy, it can quickly cause concern and deter any potential swimmers.  If left unresolved, the pool could quickly start to look, feel and smell more like a pond!

The fishy smell often indicates that the pool is not being sanitized adequately.  The smell generally stems from bacteria, algae or other growth in the water.

High levels of certain chloramines (the ‘bad’ type of chlorine) can sometimes result in a fishy smell.  The chloramines can be indicative of growth in the pool that can’t be controlled by the current amount of free chlorine.

The fishy smell can also originate from a dead animal, whether near the pool or in the pool itself.  Decaying animals can cause a pungent odor that may sometimes mimic rotting fish.

How to Eliminate Fishy Smell from Pool

A good first step in eliminating the fishy smell is to perform a close visual inspection in the pool and around it.  Ensure that there’s not a dead animal that is decaying as this could be the source of the smell.

If a nearby animal can’t be pinned to the smell, the next step is to bump up the chlorine levels in the pool to shock level.  It’s recommended that you take measurements of the water chemistry in order to calculate how much shock is needed to reach super-chlorination.

After shocking the pool, any growth in the water will be killed.  The shock should remove the fishy smell and return your pool back to normal.

Pool Water Smells Like Chlorine

A common misconception amongst swimmers is that if pool water smells like chlorine it must be clean.  Instead, the opposite is often true.

That typical “chlorine” or “pool” smell is often a result of chloramines (a.k.a. combined chlorine), which can occur when ammonia contaminants react with free chlorine. Ammonia in the pool can come from a variety of sources, including urine, sweat, and body oils.  

Chloramines reduce the effectiveness of free chlorine in the pool, which can increase opportunity for unwanted growth.  The stronger the smell of chlorine the higher chance that the pool water may not actually be clean or balanced.

Pools that strongly smell of chlorine may cause swimmers and swimwear to leave the water smelling like chlorine.

For indoor pools, it’s possible that a chlorine smell may be more noticeable due to poor ventilation.  Nonetheless, a strong chlorine odor at indoor pools –including hotels– likely still indicates high levels of chloramines and subpar sanitization.  

How to Eliminate Chlorine Smell from Pool

Now that we’ve established that a chlorinated pool should not actually smell like chlorine, we can look at how to address the situation.  

While it may seem counterintuitive, the best way to eliminate the chlorine smell is to dump in more chlorine!  

Since the chlorine smell is a result of free chlorine being expended through reactions with ammonia and other growth, it’s necessary to shock the pool in order to fully destroy the unwanted substances.  

Shocking the pool will burn out the chloramines through oxidation, thus helping to eliminate the chlorine smell from the pool.

Salt Water Pool Smells Bad

Salt water pools are designed with a salt chlorinator that converts salt to chlorine.  Many swimmers find the salt to be gentler on the skin than traditional chlorine.

Similar to a properly balanced chlorine pool, there shouldn’t be any odor associated with a salt water pool.  If the salt water pool smells bad, then it’s likely that the pool chemistry is out of balance.

An imbalanced salt water pool can have similar foul odors as a chlorine pool, including musty, fishy, and rotten egg-ish.  In some cases, a salt water pool can carry a strong chlorine odor to it as well.

In the event that any of these smells are occurring, one of the first steps should be to check the pool chemistry.  In particular, free chlorine, pH and cyanuric acid should all be evaluated to ensure they are within range.

More often than not, the bad smelling water can be cured through super-chlorination or shock.  This will burn off any compounds that are causing the smell.

How to Prevent Pool Water from Smelling Bad

When pool water smells bad, it means that you’ll need to be reactive in addressing the situation.  Fortunately, it’s possible to be proactive in preventing the situation from occurring in the first place.

Here are some measures you can take to keep the pool water from smelling bad:

Maintain Water Balance

Maintaining proper pool chemistry is the number one way to keep the pool from smelling bad.  While there’s a whole slew of different aspects to pool chemistry that can be overwhelming, there are a few key ones that can be focused on to help keep odors away:

1 – Free Chlorine

Ensuring adequate free chlorine is available in the water will help prevent growth.  This should be measured every few days.

2 – Cyanuric Acid (stabilizer)

CYA can impact the effectiveness of free chlorine.  High CYA means more free chlorine is needed.  In general, a pool should aim to have at least free chlorine that is 7.5% of the CYA.

Cyanuric acid should be measured when opening the pool and after any significant drain/refills or addition of stabilizer.  Once stabilizer is in the pool, it can only be removed through draining and refilling.

3 – pH

pH should be checked at the same interval as free chlorine.  High pH can reduce the effectiveness of free chlorine, which could allow for growth and eventual odors.  pH should be maintained at 7.2 – 7.6.

Regular Cleaning

It’s important to routinely clean the pool in order to remove organic matter and prevent its accumulation.  Cleaning includes regular skimming, vacuuming, and brushing of pool surfaces.

If large quantities of debris are allowed to break down in the pool, this will consume the free chlorine and allow potential odors to form.

Shock Treatment

Applying a shock treatment is useful if you suspect early signs of growth in the water, high amounts of chloramines, or after heavy precipitation.  The high chlorine levels will kill any growth and will reduce the chloramines.  

If water chemistry is kept properly balanced, shock treatment should not need to be a routine activity.

Proper Circulation

Proper circulation of water is important in maintaining a clean pool and preventing odors from arising.  Water circulation helps distribution of sanitizers and ensures the water is filtered.

If the pump is not run long enough each day, sanitizers may not be distributed across the entire pool allowing for potential growth.  Owners should aim to run the pump long enough to achieve at least one complete turnover of water each day.

Circulation can also be affected if the filtration equipment becomes clogged with debris, as it will reduce the amount of flow through the system.  It’s important to routinely clean the skimmer basket and filter as debris accumulates.

Final Takeaway

When a pool smells bad, it can often indicate an underlying problem.  Generally a pool should not have any odor –even that traditional “pool” or “chlorine” smell is not really a good sign.

Whether the odor is musty, fishy, rotten eggy or something else, the root cause is often due to inadequate sanitization. Aside from an odor, the underlying cause could quickly escalate to the dreaded green pool if left untreated.

When in doubt, shock it out!  Although it’s best to measure the pool chemistry, including chlorine and cyanuric acid levels, to determine just how much shock is needed.

Establishing an appropriate pool care routine will help prevent these odors from coming about in the first place.  This will keep you and your swimmers odor-free throughout the summer!

Happy (Odorless) Swimming!

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