Why Does My Aquarium Smell? + How to Get Rid of It!

All fish tanks have a slight smell. If you have a freshwater tank, it will have an earthy aroma, which is completely normal.

If you have a saltwater tank, it will have a slight ocean scent.

However, if you start smelling rotten eggs throughout your house, then it’s time to worry and address the nasty odor.

Read more to learn about all the reasons why your aquarium might smell and ways to remove the smell.

Reasons Why Your Aquarium Smells

There could be multiple reasons why your aquarium smells.

Below are some of the common reasons and possible solutions to get rid of the smell from your aquarium.

Smell Caused by Dead Fish

Fish tank owners know how common this is. The bad smell coming from your tank can very easily be a fish.

A rotting fish is bound to stink and fill your whole room with a bad smell.

If your fish tank has a lot of plants and decorations, it might be a little hard to spot a dead fish.

Some fish tend to hide behind rocks, which is another reason you might not spot them at first.

When checking for dead fish, check behind every plant, decoration, and rock. Fish can easily fit in tight spaces, so there is a huge chance you might find them there.

Also read: How to Dispose of Dead Fish (the right way)

In a few cases, your dead fish might not even be in the tank at all. Fish like killifish can easily jump out of aquariums if they don’t have a lid.

If your fish has jumped out, it will die soon and start rotting in your room.

If you sense a rotting smell but can’t find anything in the tank, check behind your aquarium and the furniture in your room.


A dead fish is an easy smell to get rid of because the smell will go away when you remove the fish from the aquarium or your room.

It is also one of the worst smells your aquarium can emit, so make sure to remove it as soon as possible.

If many of your fishes are dying, make sure to check the temperature of your water (it might be too hot or too cold), change your water regularly, and keep your aquarium maintained to provide your fish with a healthy environment.

You can also create an aquarium lid at home to cover your aquarium.

Overfeeding Can Cause Smelly Aquariums

No fish owner wants their pet to starve, but try not to overfeed them. This is also one of the biggest reasons why your fish tank may smell.

What a fish owner might not realize is that just like us, fish have an appetite.

Your fish are going to eat a certain amount of food in one feeding session and whatever they don’t eat will simply fall to the bottom of your aquarium.

This food will start to rot and produce an odor.

As the food breaks down, it releases different gases, which can cause a horrible smell in your home. The smell only gets worse as the uneaten food keeps building up.


Make sure that your tank is maintained and is in good condition.

This includes cleaning the filter, using gravel, and obviously, removing fish food from the bottom of the aquarium.

Try not to feed your fish too much – give them the amount of food they might eat in one go.

Different fish have different appetites so keep that in mind when you are feeding your fish.

Fecal Matter Can Get Collected at the Bottom

It is natural for fecal matter to collect at the bottom, which can result in a stinky smell.

This can be easily removed when you’re cleaning your aquarium but the more fish you have, the more cleaning you will have to do.

If you have a lot of fish, you might have to clean every 3 days instead of a week to prevent the aquarium from smelling.


Besides cleaning your fish tank regularly, make sure not to overstock it.

Only keep fish that fit in your tank and make sure that there is enough room in the tank for them to swim in.

If you’ve recently bought an aquarium, it might be hard to determine the right number of fish for your aquarium.

If your aquarium is already overstocked, either remove some of your fish or get a bigger tank.

Rotting Plants

The least common cause of a smelly aquarium is rotting plants. Rotting plants can smell really bad and will definitely stink up the whole room.

The good thing is – dead plants are pretty easy to spot because they turn black or brown.

Dead plants can also ruin the water, so it is best to remove them as soon as you come across them.

If you have a plant that only has a few dead leaves, you can pluck them out and let the plant stay inside the aquarium.

If you haven’t cleaned your aquarium in a while, it is prone to algae, which are also plants. Algae can rot and produce a horrible odor, so be careful!


Plants only rot when they’re not taken care of properly.

Try to keep as many plants alive as possible. Make sure your aquarium has sufficient light and the right nutrients that the plants need.

This does not mean that no plant will ever die – if they do, simply remove them while cleaning your fish tank.

Dirty Filter

An aquarium filter can get dirty very easily.

It can suck fecal matter, dust, food, and even plants.

Since it’s the filter’s job to keep the water clean, it ends up sucking everything, which means sooner or later – your filter will start smelling.


Cleaning a dirty filter should simply be part of your cleaning routine. If you haven’t cleaned your filter in a while, make sure to do it as soon as possible.

Rinse the filter media in the water when you remove it so that you don’t kill any beneficial bacteria that might be living in it.

If you clean your filter regularly, it won’t smell and will also last a long time.

The Substrate/Sand Can Smell When Not Cleaned

If your aquarium smells like rotten eggs, then the smell is probably coming from the substrate.

Substrates can smell when waste gets trapped.

If the waste is not removed and is stuck there for a very long time, it decomposes and turns into different gases that produce rotten smells.


If you regularly clean your aquarium, you’re probably good.

Some waste might be hidden behind rocks, so make sure to use a vacuum in your tank thoroughly.

If your sand is stirred regularly, it can prevent waste from accumulating and reduce the chances of a rotten smell.

Water Conditioner

The water conditioner that you will add during your water change could also be causing a bad smell.

However, the smell will slowly fade away over time, so you don’t have to worry about it too much.


A good idea is to avoid water conditioners that have smelly ingredients like sulfur.

Sulfur is the reason why your water conditioner may smell like rotten eggs.

Important Tips to Remember If You Don’t Want Your Fish Tank to Smell

Below are some tips to keep in mind to make sure your aquarium doesn’t smell too bad

Ensure Regular Maintenance

It is very important to clean your aquarium regularly. Here is what you have to do to prevent your aquarium from smelling.

Don’t forget to wipe down the glass and the edges because it is very common for algae to form in the corners.

Clean your substrate so it doesn’t collect any waste and remove all the dead plants.

Clean the rocks and the decorations because they might have fecal matter on them.

Make sure to clean your filter’s inflow and outlet. Rinse it if you feel like there is gunk trapped in it.

Remember that cleaning your aquarium regularly will prevent it from smelling.

If you are cleaning your aquarium after a long time, there is a huge chance that it will smell worse after you’re done cleaning it.

This is because when you remove all the rotting fecal matter, food, and other waste, it will float in the water.

Make sure to change the water immediately to prevent the smell from lingering and spreading in your entire room.

Change Water Daily

A good idea is to clean the water regularly.

Emptying the tank takes time, so you don’t have to do it every time, but make sure to at least clean the water.

This will keep your aquarium odorless and also remove smelly water that might be present because of waste.

Related Article: How Often to Change the Aquarium Water?

Add a Carbon Filter

Carbon filters are not a necessity, but they are great for absorbing bad smells.

Whether it’s waste or leftover food, carbon filters are known to remove odor from your water and keep it clean.

Keep in mind that if you do invest in a carbon filter, you’ll have to replace it regularly every month.

Once the carbon filter has absorbed all that it can hold, the bad smell will return, so make sure to replace it regularly.

Related Article: How Long Does Carbon Last In Aquarium Filter?

As discussed, there are various reasons why your aquarium may smell.

If you want to get rid of a smell, you have to identify what is causing it. After you have identified the cause, make sure to follow the steps mentioned above and you’ll be good to go.

Happy Cleaning!

You may also like the following articles about aquariums: