How to Remove Fish Tank Smells: A Step-by-Step Guide

Estimated read time 12 min read

There may be some bad smells in your fish tank. This can be due to a number of reasons.

In this article, you’ll find out what causes your fish tank to smell as well as a few helpful tips on how you can get rid of these bad smells.


Does a Healthy Fish Tank Smell?

A healthy fish tank is usually odorless. Fish tanks don’t emit any smells unless there’s something wrong within the fish tank environment.

What Should a Fish Tank Smell Like?

A clean fish tank shouldn’t have an unpleasant odor emanating from it. Under normal circumstances, it should have a very mild earthy smell, more like soil that has been freshly tilled. Even this pleasant smell should be very mild – so much that you should only be able to detect it when you’re working on your aquarium.

Common Reasons Aquariums Smell Bad

If your aquarium is stinking, even slightly, it’s a clear indication that something’s wrong with your tank. An aquarium may smell bad for many reasons. Some of the most common ones have been listed below:

Dead Fish or Something That Has Died

One of the most common reasons for a fish tank stinking is dead fish or the death of any other creature in your fish tank like a snail. The stench is so pungent that it’ll dominate the air of the room if you’re away for a few days.

Detecting a dead fish in an overly-populated or highly decorative aquarium can be pretty tough. A fish may die in a hide-out or behind an aquarium accessory. It’s so difficult to find dead fish that you may not even realize that a fish has died until a few days after it has started decomposing.

When a fish dies, its body releases oils and proteins that produce a strong, disgusting stench.

One way to prevent your tank from smelling like dead fish is to do a fish count every few weeks. If you’ve counted fewer fish than you usually have, immediately check to see if any have died somewhere in the aquarium.

Overfeeding & Uneaten Food (Ammonia)

Fishes have a small stomach and can only eat a small amount of food. So when you overfeed them, they’ll only eat enough to fill their stomach and leave the rest. The leftover food will settle at the bottom of the aquarium and serve as a buffet for bacteria.

The bacteria will feed on the uneaten food and grow large colonies rapidly. These bacteria then produce ammonia. Ammonia has a powerful, foul odor – which is what makes your fish tank smell terrible.

Preventing Smells Caused By Rotting Food

The best way to prevent smells caused by rotting fish food is to feed the fish with the amount of food they quickly eat and remove the leftover food after a while. It’ll prevent the food from settling at the bottom, thereby preventing the growth of ammonia-producing bacteria.

Fish Poop

Fish eat food, and naturally, excrete it, too. The bacteria in the fish tank feed on the fish waste, and filters tend to filter it all out, hence preventing it from piling up in the tank. However, if there are too many fish in your aquarium, the bioload will be too much for the bacteria to handle.

Excessive accumulation of biowaste is one of the major causes of a smelly fish tank.

Preventing Smells Caused By Fish Poop

While you can’t stop fish from excreting, you can indeed prevent the smells caused by fish poop. The first thing you should do is measure the dimensions of your aquarium and make sure the number of fish isn’t more than the number recommended for your aquarium size.

Secondly, perform a 20 to 30% water change to eliminate the overwhelmingly dominating fish poop smell. Again, it would be best to complete one every other week. Thirdly, ensure that the filter is of adequate size for your aquarium and isn’t clogged with aquarium waste.

Rotting Plants and Organic Matter (Ammonia)

Most aquarists add live plants to their aquariums. Not only does this look aesthetically appealing, but it also provides a healthy environment for the fish. However, as beneficial as live aquarium plants are, a dead plant can produce strong (and often unpleasant) smells.

Preventing Smells Caused By Rotting Plants

You can prevent smells caused by rotting plants by inspecting the aquarium plants regularly. When aquarium plants die, they turn brown or black and may even make the aquarium water appear become turbid. So remove dead plants as soon as you see one.

Dirty Filter or Old Media

Another reason why your fish tank smells so bad is a dirty filter or old media. Filters are responsible for filtering out the dirt from the fish tank water. The filters get dirty over time. When they get dirty, their ability to filter water anymore is significantly reduced. As a result, the water continues to get dirty and smelly. A dirty filter itself smells terrible.

If you haven’t changed your fish tank water for a while, you should expect your fish tank to smell bad. This is because the fish in the tank continuously produces waste. The leftover food accumulates constantly, and as a result, the bacteria thrive. All of this can lead to the media getting saturated with waste and becoming smelly.

Preventing Odors Caused By Your Filter & Media

Cleaning and changing the clogged filter every few weeks is a good practice that can help you prevent your fish tank from smelling bad. You should also change the aquarium media regularly. It’ll ensure that your media is clean and the filters are in perfect working order at all times.

Anaerobic Activity in Your Substrate

There are areas in your fish tank where there’s very little to no oxygen, like deep in the sand or gravel. When water movement is decreased, the crannies and nooks in the fish tank become water-deficient or dead zones. The deposition of debris is one of the primary reasons why dead zones are formed in an aquarium.

The bacteria present in these regions utilize oxygen from nitrogen dioxide present in water and release nitrogen. The process produces hydrogen sulfide as a by-product that creates a strong rotten egg smell.

Preventing Dead Zones in Your Substrate

You can prevent the formation of dead zones in your substrate by directing the water flow to these areas. The water flow will move the debris around. The activity will increase the debris being caught in the water filtration system, thereby preventing dead zones and the associated smell.

You can also place powerheads in areas that have an insufficient oxygen supply.

Air Quality and Humidity

Poor air quality and a high level of humidity can cause your fish tank to smell. If the humidity of the room you have placed your fish tank in is high, it can result in the formation of mold, which, in turn, produces a foul smell.

Water Conditioner & Other Additives

Some water conditioners and water purifying chemicals contain sulfur which may also be why your fish tank smells bad. To prevent it, avoid using water conditioners that contain sulfur as a constituent.

Ways to Freshen a Fish Tank

Don’t worry if your fish tank smells bad. There are numerous ways to freshen up your tank so that it smells not only pleasing but also looks good too.

Remove Any Rotting or Decomposing Organics

As we’ve mentioned earlier, one of the primary reasons for bad fish tank smells is rotting and decomposing dead fish, other creatures, and plants. So one way to freshen up your fish tank is to remove any of these rotting and decomposing organics – the sources of the smell – and put the alive fish back into the aquarium environment.

Clean Your Tank Thoroughly

Cleaning your fish tank regularly is very important. The accumulating debris, fish waste, and uneaten food build-up make your fish tank appear dirty and smell bad. By cleaning your tank, you’re eliminating all the sources that might make your fish tank smell bad.

Add a Carbon Filter

Installing a carbon filter to your fish tank is a sure-shot way of freshening it up. A carbon filter removes the smell and combats the discoloration of water. It also removes inorganic and organic matter from the water. As a result, all of the bad smells get trapped in the pores in carbon and get removed from the water.

Steps for Getting Rid Of Fish Tank Smells (Fixes)

If your fish tank is smelling bad and you want a step-by-step to help you through the process of fixing it, follow the steps listed below:

1: Regularly Clean Your Filter

The fish tank filter is working to keep the debris and particles from the water continuously. But, it’s bound to get dirty and even clogged if it isn’t cleaned regularly. So, the first and the most crucial step in getting rid of fish tank smells is to clean and unclog your fish yank filter regularly.

2: Change Your Water Regularly

There will always be waste, both organic and inorganic, that a filter can’t remove, like fish poop. If you don’t remove this waste from your fish tank, it will eventually produce unbearably strong fish tank smells. Change the water of your aquarium every few weeks to get rid of the fish poop, thus keeping your tank clean and odorless.

3: Make Regular Water Changes

It would be best if you didn’t wait for the fish tank water to become smelly. Instead, make it a practice to perform weekly water changes. For example, instead of emptying all the water, change only 20 to 30% water every week, or once in two weeks. It’ll keep your fish tank water clean and will keep fish tank smells at bay.

4: Don’t Overstock Your Fish Tank

One of the significant reasons why fish tanks develop foul smell is the overstocking of fish. The more fish you have in your tank, the more waste they will produce. Hence, you’ll have a fish tank that smells terribly. So always make sure that you aren’t overstocking your fish tank.

5: Clean Your Tank

While most people focus on changing the fish tank water, it’s essential to clean the tank itself. Empty your fish tank once every few months. When you’ve emptied it, scrub the walls clean.

Mold and slime may stick to the glass walls of your fish tank. Algae makes your fish tank look dirty and contributes to the fish tank smells as well.

6: Clean Your Gravel and Rocks

Fish poop and leftover fish food may settle into the gravel and rocks. You may not be able to see because of the colors and textures. But over time, this organic waste starts to decompose and produce strong fish tank smells that you can’t stand,

Make it a practice to take out all the gravel and rocks from your fish tank and wash and dry them thoroughly. Even replacing them with new ones after a few months is a great way to ensure the fish tank doesn’t smell bad.

7: Clean Your Fish Tank Decorations

You may not realize this, but organic waste may get deposited on your fish tank decorations. Even if it doesn’t, they may develop slime due to being in water constantly. It’s the reason why aquarium decorations lose their original appearance after only a few days of being in the water.

This may be a cause of your strong fish tank smells and the water turning cloudy. So, clean your fish tank decorations every time you’re changing the water.

8: Clean Your Fish

When you’re changing your aquarium’s water, transfer all the fish to a tub of clean water. Ensure to include some water from the fish tank to prevent exposing your fish to fish stress since they’ll be in an entirely new environment. It may be fatal for your fish.

9: Add Bacteria to Your Tank

It may come as a surprise to you, but certain bacteria are beneficial for your fish tank. These bacteria feed on the fish waste and prevent the development of foul fish tank smells. In addition, they keep the fish waste from accumulating.

These beneficial bacteria feed on dead plant material, fish waste, and other types of organic debris found in the fish tank. They help maintain the clarity of fish tank water. Above all, beneficial bacteria prevent the accumulation of toxic nitrite and ammonia.

10: Fish Tank Deodorizers

As you can tell by the name, fish tank deodorizers are deodorants for the fish tank. They mask the fish tank smells. Carbon deodorizers even absorb the scents and keep your fish tank smelling pleasant – similar to freshly tilled soil.


How to Remove Anaerobic Bacteria Smells?

If you want to eliminate the anaerobic bacteria smells from your fish tank, perform a 50% water change. Also, make sure to clean your fish tank every week.

Why does my fish tank water smell like rotten eggs or sulfur?

A rotten egg smell or sulfur smell in your fish tank indicates a severe bacterial imbalance or build-up, a problem with your fish tank filter, a chemical imbalance. In this case, you should change the water in your fish tank and treat the water with a water conditioner and deodorizers.


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