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Why Does Your Fish Tank Smell Like Rotten Eggs? 4 Reasons Why

It’s all fun to have an aquarium at home until it starts stinking. Healthy fish tanks are usually odorless. Having a nasty smell clearly indicates there is something wrong with your aquarium that needs to be addressed immediately. To get rid of the bad smell, you first have to find its cause. Don’t know how to do it? Don’t worry, we are here to help you.

Why Does The Aquarium Stink Like Rotten Eggs?

why does my fish tank smell like rotten eggs
The rotting eggs smell is sulfur dioxide gas. It usually collects in an aquarium and causes a foul odor when there is a serious bacteria buildup or a chemical imbalance in the water. A decaying dead creature, plant, uneaten food, and excessive fish poop are usually responsible for the smell. A dirty fish tank and equipment can also give rise to it.

Let’s talk about all the possible reasons that cause a fish tank to smell like rotten eggs or worse.

Something is Rotting

In a fish tank, there are a number of things that tend to rot and put off an unpleasant odor. It could be a dead creature (fish, snail, or other invertebrates), a live plant, or uneaten food.

When a decaying matter goes unnoticed and stays in the water for long, it starts rotting and causes a foul smell.

Fish Poop

The role of fish in an aquarium is to eat, swim and poop. And the job of the filtration system is to take the waste out of the water, ensuring the cleanliness of the environment. In case your filter is not doing the intended job well, you are going to have the fish poop accumulated over the substrate causing the tank to stink.

Furthermore, it is the beneficial bacteria in the tank that breaks down the organic waste and keeps it from causing harmful effects. But if your aquarium is heavily stocked, it will result in excessive accumulation of the biowaste contributing to the unpleasant odor.

Water Quality

Another reason your fish tank smells terrible could be due to issues with water. Aquarium’s water quality is usually degraded when there is organic waste or it is exposed to unnecessary chemicals. It imbalances the water chemistry and gives rise to a foul smell one can’t stand.

This is why water changes are crucial: they help keep the aquarium clean and free from dissolved toxic waste.

Improper Cleaning

why does my fish tank smell like rotten eggs
This is self-explanatory. A fish tank that isn’t cleaned regularly will stink after some time. When you have living creatures in a tank eating and pooping daily, it’s crucial to keep their environment clean. It means doing periodic water changes, keeping the decor and equipment clean, and scraping algae off the sides of the aquarium.

How To Get Rid of Fish Tank Smell?

To get rid of your aquarium smell, first, you have to identify its source and then take the necessary measure.

Take a look at your fish and other decaying critters (snail or other invertebrates) and make sure none of them is missing. If numbers don’t match up, check behind the decor, rock, and plant. Examine all nooks and crannies. Even check your filter system as these tiny creatures often get stuck on it.

Your pet might be fallen sick or have died there in the hide-out and causing terrible odor. If you have a crowded tank, then you might not even notice any missing creature until it starts stinking.

Also, make sure you don’t have any plants rotting underwater. To identify the dying plants, look at those with distorted leaves and take them out of the tank.

Uneaten food left from overfeeding is another organic matter that discomposes and releases a horrible smell. So check around the lip at the top of the tank and remove any bits of food you find floating. As soon as you identify the decaying matter and remove it, you will be able to get rid of the bad odor.

Rotten egg smell is gas pockets (usually sulfur dioxide) building up in the substrate. So doing a huge gravel stir will help release the gas and make your fish tank stink-free.

Another factor that majorly dictates the odor of an aquarium is the water quality. Make sure you do 10-15% of the water change each week. If you have a heavily crowded community tank, you can go for 25% for optimal results. Do not put unnecessary chemicals in the aquarium, and especially avoid conditioners that are high in sulfur.

Last but not least, clean your fish tank and equipment regularly if you don’t want it to smell bad. You can’t risk being lazy when it comes to periodic cleaning of the tank as it involves the life of your aquatic pets.

What Does a Healthy Aquarium Smell Like?

why does my fish tank smell like rotten eggs
There are different descriptions as to how a healthy fish tank should smell. An aquarium with a mild earthy aroma is considered to be good. It’s a very light odor, like freshly plowed earth. To know what this smell feels like to your nose, you have to get close to the water and sniff. You shouldn’t find it fishy or even slightly pungent.

Many aquarists claim that this slight aroma comes from the nitrifying bacteria used for the nitrogen cycle in an aquarium.

Tips to Keep Your Fish Tank from Stinking

  • Perform regular water changes. Tanks with less bioload can do 15% of the water every week. Whereas crowded fish tanks require at least 20 to 30% of water change each week.
  • Do not overfeed your fish. And remove all the leftover food once your fish is done eating.
  • As we know, creatures dying in the tank and rotting is one of the main reasons for foul smell. If you have experienced many such instances, you should do a fish count every week. Anytime numbers don’t match, you know where to look for the dead ones and remove them before they make your whole aquarium stink.
  • Do not treat the tank water with conditioners that are high in sulfur. The rotten eggs smell is precisely the sulfur dioxide gas building up in the aquarium.
  • Clean your aquarium and its content regularly. Decor, gravel, and rocks are where most waste gets piled up and causes a bad smell.
  • If you have live plants in your aquarium, always keep an eye on the dying plants and remove them as soon as you see their leaves turning brown or yellow.
  • Add a carbon filter to your aquarium. It is an effective way to eliminate foul odors.
  • Avoid overstocking your tank.

Frequently Asked Questions

Is air freshener toxic to fish?

It is not recommended to use such products near an aquarium as they contain chemicals that can be harmful to your aquatic pet.

What to do for the lingering dead fish smell?

Even after removing the dead fish, if the nasty smell isn’t going, do a 50% water change and perform it for a couple of days.


We hope with the methods given above, you are able to get rid of the foul smell that is coming out of your aquarium. Simply identity and cause and take the required measures – that is all you have to do.

If you fail to detect the source of the smell, we suggest you seek professional help. You can contact your local fish store to help you remove the stink.