8 Reasons Why Does My Fish Tank Smells Like Sewage [+Bonus]

Why Does My Fish Tank Smells Like Sewage

Top Reasons Why Does My Fish Tank Water Smells Like Rotten Eggs

If you place your nose directly over the filter of the aquarium, you will find that almost all fish tanks are comparatively odor-free. Although, sometimes fish tank owners report extremely smelly fish tank water. Sometimes their fish tank smells like sewage.

If you are able to find an aquarium using solely your nose, there’s something wrong. Rapid attention is indicated when you find fish tank smells.

If I’m not wrong, a healthy aquarium can have a very slight smell. No, it is not like a fishy smell. Instead, a smooth and pleasant smell. However, here is how fellow aquarium owners explain their fish tank smells…

  • Freshwater tanks– A smooth and mild earthy aroma, like freshly plowed soil
  • Saltwater tanks – Slightly ocean scent, just like the beach

Typically what you’d call it as bad smells, right? I mean, you’ll purchase candles with these scents! One important thing I need to stress is that these scents are not so strong and effective. You never have to shut your eyes and guess that there’s an aquarium within that area or room.

If you are able to smell your aquarium from across the room/area, and it stinks, there might be something seriously wrong with your fish tank.

Here, I’m going to take you through all those typical reasons for the smells as well as how to keep a fish tank from smelling from any smelly fish tank.

Why Does My Fish Tank Smell or Stink?

A properly well-maintained fish tank isn’t likely to ever develop an overwhelming fish tank smells, as unhealthy odors are sometimes caused by bio-waste (decomposing biological material) which is cleaned out.

Leftover fish food that is rotting under the aquarium water or high amounts of normal fish poop is often the main culprit of fish tank stinks. However, decomposition plant material may also be accountable.

Main Causes of Bad Fish Tank Smells

Following are some sources of decomposing biological material or bio-waste:

1. Something Died in The Tank

One of the most common reasons for a stinky fish tank can be a dead fish in the tank. It may be so many days following the death of a fish before the aquarium owner realizes something is wrong.

The dead fish may have hidden in an out of the way corner of the dirty fish tank and died silently, leeching oils and proteins which float to the surface and evaporate. Quickly locating the dead fish body and removing it from the tank should eliminate fish tank smells.

I don’t like to break it to you; however, that bad fish tank smells coming from your aquarium might be the remains of your much-loved fish. A rotting fishstinks.It might fill your room with a terrible odor.

If you’ve got a tank filled with plants or decorations, a dead fish could not be easily spotted. Also if you own a crowded community aquarium, a missing fish can’t be easily noticed.

I once had a typical pleco that was shy and it only came out in the dark. The pleco spent his days hiding in the corner of the aquarium. Time passed by without me seeing that fish.

One day I noticed my fish tank smells musty and it coming from my aquarium. After investigation, I found his rotten body deep inside his favorite concealing spot.

Now, it is time for roll call some fish. If any fish is found missing then it could very well be the source of the horrible fish tank smells. Make sure to check behind every decoration, plant, and rock. You’d be astonished at the tight areas of the tank that fish will squeeze themselves into.

The dead fish may not even be found in the aquarium at all! It is normal with jumping fish, such as killifish, which may simply leap out of foggy fish tanks that do not have any lid. Needless to mention, a fish out of tank water will not last for a long time and it will soon start to stink.

If your fish is a jumping fish, check behind your fish tank stand and under any close furniture to find the fish’s body.

A dead fish has a mild smell to control. The bad fish tank smells should soon disappear once the fish is removed from that room.

How to Stop Bad Smells Caused By Dead Fish

Unfortunately, this is often the hardest form of smell to manage if your fish tank smells bad and is cloudy – no fish lives in the tank forever. Though it is sad to hear, it is true.

One best thing you’ll be able to do is to provide your fish a healthy and long life by getting their necessities right.

Best water quality, proper diet, not overstocking, and regular maintenance go an extended way to see your fish living a full happy life.

2. Stop Overfeeding

Another common reason for bad odors from the aquarium is overfeeding. Unconsumed food falls to the bottom of the aquarium, wherever it develops an overgrowth of bacterial or microorganism colonies. As exponentially the bacteria grows, those leftover foods release waste gasses that contain a foul odor.

I am pretty sure you don’t want your most loved fish to starve, however, overfeeding is probably one of the worst things you can do to the fish. It can also be liable for the terrible fish tank smells that are coming from your fish tank.

Look… Your fish are solely going to eat such a lot of food in one feeding session. Any amount of food that is unconsumed falls to the bottom of your fish tank and starts to rot.

As the uneaten food breaks down inside the aquarium, it releases bad gasses, causing horrible fish tank smells. This terrible smell becomes stronger as this unconsumed food builds up.

A good aquarium maintenance routine, like using a gravel vac and filter cleaning, must remove most of the traces of decaying fish food and the foul odor along with it.

How to Stop Bad Smells Caused By Excessive Fish Food

It is very easy in reality– only provide your fish with the quantity of required food they eat in one session. In this manner, there’ll be no fish food left to allow off bad smells.

Figuring out simply what proportion needs trial and error on your part – with numerous different types of fish food and different species of fish ‎, the actual quantity will vary dramatically.

As a rule of thumb, feed your fish only as much as they can eat within 5 minutes.

3. Fish poop is Another Reason

That terrible fish tank smell might also, be caused by the food that your aquarium fish do consume. If your fish tank is being stocked in the right way, you’ll follow your daily aquarium maintenance routine far before the fish poop starts to stink up your aquarium.

As you’re likely cautious:

The More Fish = The More Poop

The built-up fish poop breaks down fast. As it breaks down, it provides off horrible fish tank smells.

How to Prevent the Bad Smells That Caused By Fish Poop

There is a simple way to fix it! Never overstock your aquarium. Only keep those fish that are right for the size of your fish tank. Overstocking is an issue.

It is usually faced by beginner fish keepers initially who don’t have any idea of fish keeping. Before you purchase any fish for your fish tank, ask an expert for their opinion or use a stock calculator.

If your aquarium is overstocked currently, then you have 2 options:

  • Remove some of your fish from the overstocked aquarium
  • Purchase a larger tank

4. Rotting plants in Your Aquarium

As compared to decomposing oils and proteins this is less common. A rotting plant even under the aquarium water may release a terrible stench when left abandoned.

Fortunately, dead plants can easily be spotted. They usually turn a slimy black or brown color and foul up the quality of tank water with murky, turbid water.

It is necessary to spot and remove dead plants from your fish tank.

Though it is less common as compared to the other reasons on this list, one rotting plant may provide off one heck of a stench if it is left unwatched. Dead plants are simple to find out. These plants no longer seem like themselves and usually turn a slimy black or brown color.

You must remove the dead plants from your tank anyway, the reason is they also foul up the quality of water. If there is a plant in your aquarium that only has a few dead leaves, some light pruning is all it receives to pluck its rotting bits.

And bear in mind, algae are also plants. Algae may rot and leaving you with a terrible musty odor. Blue-green algae especially may make your fish tank smell very funky.

How to Prevent Bad Odor Caused by Aquarium’s Dead Plants

The first and foremost thing is to keep them alive! Any living plants do not give off horrible bad smells. I believe it is often easier said than done. However by making certain, the plants have sufficient nutrients and light, you provide them the simplest chance to thrive in your storage tank.

Else, why not invest in a clean-up crew for the aquarium? Malaysian trumpet snails easily devour any decaying or dead plants with no effort on your half.

I have had live plants from the very beginning of fish keeping. Typically the leaves can die back. I will simply notice the leaf. If the leaf doesn’t bounce back within a few days, I’ll clip the leaf even though it dies only 50%.

The only reason you are taking out dead leaves particularly ones that have fallen off the stem. It is because it deprives the nice plants of so much required nutrients.

Plant leaves in your fish tank which is still hooked up deprive the remainder of the plant of actual nutrients as well as oxygen. Its reason is the plant is still in a struggle mode trying to heal the unhealthy half of it using most of its starches or energy to improve the health of the bad side.

However, yet it starts to deprive the remaining of the plant or starts the process of weakening the plant’s any part which can be in a weak position.

If the leaves of the plant are on the aquarium’s gravel, fully detach it from the plant. As in the case of your aquarium – the leaves may start to produce bacteria or mold inside of the aquarium. The dead brown leaves are simply that, dead.

Does it create any sense to leave something dead lying around? Unless otherwise, you’re making a compost site at the bottom of your aquarium, what sense is it to keep anything like dead plant leaves in your fish tank? Do you keep dead fish in an aquarium?

Believe it or not, dead fish or dead leaves are almost equal…each of them produces bacterial conditions. Just throw away any part of dead leaf and clip off any 50% or higher of a dying leaf hooked up to the stem of a live aquarium plant.

5. Dirty Aquarium Filter

Do you know every item mentioned so far? Well, each one of the items may be sucked into your aquarium filter system.

Even, it is very common to search out a lot of rotting sludge within the filter than in the fish tank itself. After all, the task of a mechanical filter is to assemble any sludge which is floating through your fish tank and arrange it in one place.

Due to this reason, filters may smell bad. Really horrible!

How to Prevent Bad Smells Caused By Your Fish Tank Filter

I will be straight up – cleanup the aquarium filter must be a part of your regular maintenance schedule…

When the time comes to change your aquarium water, rinse the filter media in water that you removed so that you do not kill any good bacteria which are living thereon.

By doing so it should remove the majority of the stinky sludge which has been stinking up the filter joint.

6. Aquarium Substrate

If the bad horrible odor coming from your fish tank and smells like rotten eggs, then the substrate could be at fault. It just smells… This is a quite complicated concept, so here is the starter-friendly explanation:

Very fine gravel or sand that has compacted over time can create zones where there is zero oxygen. In these pockets, bacteria convert it into gases when waste gets trapped. Just smelly gasses!

This type of gas then rises up throughout the fish tank and enters straight into your nostrils!

How to Prevent Your Materials from Releasing Bad Smells

Here again, maintenance is the king of the game. Regularly stirring sand or a deep gravel vacuum can stop these extremely smelly pockets of gas from creating up in your fish tank.

I suggest you read up on how to maintain it before you choose a substrate for your aquarium!

7. Fish Tank Odor Eliminator (Aquarium Water conditioner)

The water conditioner that you add at the time of your tank’s water change might also be responsible for creating your aquarium smell funny.

Let’s take my most favorite fish tank odor eliminator Seachem Prime that I use in my aquarium. When you open the cap on the conditioner bottle there is no mistaking the eggy smell it provides off.

But, when you add the fish tank deodorizer to your aquarium water, the aquarium smell easily fades away to the point of being unnoticeable.

How to Prevent Bad Smells Produced By Aquarium Water Conditioner?

Always avoid aquarium water conditioners with smelly ingredients such as sulfur. This is often the reason for that rotten egg smell coming from your fish tank.

8. Wastes from an Overstocked Fish Tank

An excessive amount of bio-waste also can be the result of overcrowding. Overstocking the aquarium implies that so many fish are living in a very small volume of aquarium water.

Once fish eat, they create excrement. As the quantity of fish goes up, so does the tank’s fish poop. Eventually, the overabundance of waste in the aquarium is very much for tank filters, beneficial bacteria to process.

How to Prevent Bad Smells Caused By Wastes from an Overstocked Fish Tank

The best rule is to possess not more than 1 inch of fish per gallon of water. This rule is for smaller fish like betas and guppies. Larger fish will require almost 3 gallons of water per inch.

Don’t forget to take into account that the majority of your fish can grow bigger over time. When you are working with a normal-sized fish tank to keep the water clean with a natural cycle, you are not able to keep as much fish as they can in the big pet store.

+Bonus Steps to Remove Bad Smells

Important: Before you read this step, ensure that you have detected the actual source of your bad odor from the above-mentioned list. If you don’t remove the source, then the following techniques can’t fix the terrible odor.

How Is Decomposing Fish Identified in Your Tank?

  • Removal of Source

The first and foremost task to do is to keep and maintain a decent running stock of your fish. Are any missing? If thus, start checking out the remains, as that could be the reason for the bad smell.

Remember that some small fish are consumed by their own tank mates, thus a missing fish can never be found, however, predation will not cause any odor.

If a rotten body of a fish isn’t the main cause of the odor, and every fish are accounted for and present, then the issue is probably because of a buildup of organic material on or in the aquarium gravel.

Dislodge fish tank furniture to search for particles of unconsumed food and plant remains. Use a tank scoop or vacuum to clean the substrate (ground material) either outside or inside the tank.

Provide the complete aquarium a decent cleansing, and then reduce the feeding regimen to at least one tiny feeding per day. It is also important to clean the aquarium filter before and after the washing process.

If there is so much debris inside the fish tank, this means that the filter has probably been clogged and not filtering perfectly for some time. After removing all those sources of bad odor, perform a smell test once again.

  • Take Preventative Measures

When you have eliminated the source of the horrible smell, wait for an hour or two and use your nose to sniff once again. Once all bad smells are gone, there are few steps to take to confirm your aquarium smells clean.

Feed your pet fish sparingly. If you do not stop feeding your aquarium fish entirely, they’ll not die of starvation. Even, fish will and can suffer a range of disorders if they’re overfed.

Schedule tank cleanings and regular water changes. Every fish tank is a closed atmosphere, thus cleaning is an absolute need to have a healthy environment. Usually, fish tank smells are the cause of slow growth in bio-waste by-products, it is because of skipping or never performing a water change.

Step 1: Aquarium Maintenance

First of all, you would like to clean your aquarium. Your goal is to get rid of each piece of rotting organic matter in your fish tank.

When making an attempt to know how to get rid of the fish tank smell, I extremely suggest being much thorough than during a regular maintenance schedule. Thus, put aside additional time to try and do the following:

  • Wipe down the aquarium glass
  • Clean the substrate
  • Prune any dead leaves off-tank plants
  • Clean any decorations or rocks
  • Clean your filter outlet and inflow
  • Perform a partial water alteration
  • Rinse your filter to get rid of trapped gunk

… And any other care and maintenance steps that are unique to your aquarium. If it seems like a rotting substance, and it does not belong to your aquarium, you just remove it!

If you do not have performed any maintenance within some estimated time, it is very likely that the aquarium will smell worse after you clean the fish tank.

The main cause for this is that you are dislodging all the rotting substance, permitting it to float freely in the aquarium water. This could only be temporary.

By observing the water quality of your aquarium with a test kit, and sticking to a very hard maintenance routine, you can remove the bad odors in zero time.

But to speed the method up…

Step 2: Daily Tank Water Changes

Over the subsequent few days, perform a change of water 10-15%. This can add odorless and fresh water to your fish tank when removing some of the foul-smelling water from your fish tank.

Step 3: Add a Carbon Filter in Your Tank (Optional)

While cleansing, remember the filter. It is recommended to use activated carbon media in the filter to help remove odor-causing ions (molecules), however, note that the sufficient surface space in the carbon does get used up properly. That has to be changed several times in a year to stay effective.

While you’re waiting for the terrible fish tank smells to clear up, you may add some special ingredients to the filter to prevent the unhealthy smells in their track.

When it involves absorbing the bad smells, an activated carbon filter performs wonders. This magical substance will make your tank water clearer, removing discoloration.

Additionally, it pulls odors from your aquarium water and prevents them from reaching your nose.

The only drawback is that a carbon filter requires to be frequently replaced, at least once in a month. When the carbon has absorbed everything it can hold, the terrible smell will return.


If you’ve made it this way, you will notice a pattern to preventing bad fish tank smells.

Did you notice anything?

That’s right…

Performing Correct and Regular Maintenance!

You see, the majority of all bad smells come from rotting organic substances. With proper care and maintenance, these all should be removed far before they create up and stink up your space.

Therefore, do yourself a little favor and set up a maintenance schedule. Your nose will say thank you for it!

Have you got a tip for getting rid of bad fish tank smells? Let me know in the comments section below!


Dibyajyoti Bordoloi is the creator and author of FishCampRehab.com, a third-generation experienced fish keeper and owner of a successful pet breeding farm. He is also a member of the Center for Wildlife Rehabilitation And Conservation (Assam), the Marine Aquarium Societies of North East India, and the Kaziranga Nature Conservancy of Assam.

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