How to Stop Your Fish Tank from Smelling Bad

There are few things more unpleasant than seeing your beautiful aquarium starting to smell bad.

But don’t worry – this happens relatively often and I am here to share everything you should know about how to stop an aquarium from smelling bad, as well as how to prevent this from happening again.

In the end, a unpleasant stench not only disrupts the serenity of your personal oasis but it also raises concerns about the wellbeing of the fish and even plants living there.

Why Does Your Fish Tank Smell Bad?

fish tank smelling bad

You must identify one of the multiple factors that could contribute to your tank’s off-putting odor, which include overfeeding, a poor, dirty or underperforming filtration system, neglecting regular water changes, and failing to remove decaying organic matter.

Each of these things can drastically impact the water quality and subsequently affect the smell of your aquarium. Below, we’ll talk in depth about each one so that you can easily identify the problem to be able to quickly solve it.

Overfeeding Is Usually the Main Reason Behind a Stinky Aquarium

One of the most common and often overlooked reasons why your aquarium smells bad is overfeeding.

Feeding your fish too much or too frequently leads to uneaten food that gradually sinks to the bottom of the tank.

Here, it starts to decay and releases compounds such as ammonia, nitrites, and nitrates, which can generate an unpleasant smell.

This unpleasant smell also translates into changing water parameters, affecting the entire ecosystem and putting the life of your fish or other animals living inside the tank in danger.

This is also one of the main reasons for cloudy aquarium water, which is again one of the things you’ll notice if overfeeding is the cause of a smelly fish tank.

Moderation and observation are key to understanding how much you should feed your fish and during this learning process, it’s usually better to underfeed than overfeed.

All fish can do better for shorter periods of time without food. I wrote an in-depth article on how long can a Betta live without food and the same goes for most aquarium fish.

The golden rule of thumb here is that you should only feed your fish 1-2 times per day and not more than what they can consume in around 2 minutes.

Smelly tank due to an underperforming Filtration System

An essential part of maintaining an odor-free tank is an efficient filtration system. It serves as your tank’s kidney, removing waste, uneaten food, and toxins.

When the filtration system underperforms or fails, these unwanted substances stay in the tank, break down, and start to smell.

Therefore, ensuring the filtration system’s efficiency is a crucial step on the path of learning how to stop your fish tank from smelling bad.

This means that you should either replace your filter if it’s too old, give it a proper cleaning or simply buy a better performing one, suitable for the size of your fish tank.

If you need help deciding, I have an article about the best water filter for a large aquarium, as well as a more generic one sharing the best filters for aquariums.

Lack of Water Changes Could Make Your Fish Tank Smell Bad

Replacing some of the water in your aquarium at regular intervals is one of the key things you can and should do to keep everything running smoothly – and bad smells away.

By changing the water, you will be removing some of the substances that the filter wasn’t able to, and bring in clean water that your pet fish need and love.

Therefore, it’s recommended to replace 10-20% of your tank’s water weekly or biweekly, depending on the tank’s size and bioload. Ignoring this step leaves your aquarium in an unhealthy, malodorous state.

Don’t forget to rub away those white spots on your aquarium’s glass too, especially if you’re not sure of their origin.

Decaying Organisms: The Hidden Stench

Decaying organic matter, whether it’s a deceased fish or a dying plant, releases an unpleasant odor as it breaks down.

Dead fish, in particular, can rapidly decompose, releasing a potent stench.

Thus, regular inspection of your aquarium to locate and remove such organisms before they start to decay is an important step in the process of learning how to stop your aquarium from smelling bad.

Not to mention the fact that these decaying elements will quickly alter the quality of your water, putting your entire aquarium population at risk.

How to Stop Your Aquarium from Smelling Bad

beautiful aquarium

Despite your best efforts, there may be times when you’re confronted with an aquarium that smells bad.

Now that you have understood the potential causes and preventative measures, it’s time to talk about how to actually stop your fish tank from smelling bad.

Changing water: the first step

Usually, the first and most important step when it comes to an aquarium that smells bad is performing a partial water change.

Replace around 25% of the water if it’s smelling bad, then to another partial change of around 15-20% in 2-3 days. Repeat once more if things don’t improve.

Make sure to also look inside the aquarium and remove any obvious thing that might have caused the unpleasant odor, such as a dead fish, decaying plants or excess build-up of fish residue or food.

Fresh activated charcoal for your filter

Activated carbon, a staple in advanced aquarium filtration, is often regarded as the modern answer to how to stop your aquarium from smelling bad.

Adding activated carbon to your filter not only helps in removing color taints and medication residues but also plays a significant role in odor control.

Not all filters can hold activated charcoal and it’s not always a must to have one, but usually this helps a lot. If you already have it, probably it’s time to replace it with a new batch.

Adding Live Plants Is a Long-term Key to Less Smelly Aquariums

Live plants offer an elegant and natural solution on how to stop your fish tank from smelling bad.

They work on multiple levels – absorbing harmful nitrogen compounds, providing oxygen, and adding to the aesthetic appeal of your aquarium. They are basically an additional water filter, one that your fish will love.

I wrote about the best fish tank plants for beginners, as well as the best floating plants for aquariums if you’d like to have some of these too.

Water Conditioners

Water conditioners can be a valuable addition in your battle against bad smells. These substances detoxify harmful chemicals present in tap water, such as chlorine, and some even neutralize ammonia, nitrates, and nitrites.

I am personally against adding these chemicals into your aquarium since they can be dangerous for the fish (as it is the case of Borax, for example).

But as long as you read the instructions and you don’t overdo it, they can help your quest to quickly get rid of the bad smell in your aquarium.

Beneficial Bacteria Supplements:

Supplementing your aquarium with beneficial bacteria can also help in answering the question, “how to stop your fish tank from smelling bad?”

These bacteria, part of the natural nitrogen cycle, break down harmful waste products like ammonia and nitrites.

In essence, they help maintain the tank’s biological balance, which can go a long way in preventing unpleasant smells.

You can introduce beneficial bacteria through commercially available products, often in the form of a liquid or powder, but this is usually done early on, when setting up your tank.

Once it is more established, it’s usually better to use the other recommended methods, as this could end up in messing up your water parameters. But it could work for new fish tanks.

Ozone Generators and UV Sterilizers: The Technological Titans

Last but not least, for those who prefer a high-tech solution, ozone generators and UV sterilizers offer an advanced way to keep your aquarium odor-free.

Ozone generators break down organic waste at a molecular level, neutralizing bad smells, while UV sterilizers kill harmful microorganisms and algae that could otherwise contribute to the bad smell.


An odor-free fish tank is a sign of a healthy and thriving aquatic ecosystem. By understanding the causes of the odor and adopting preventive measures, one can maintain a clean and pleasant aquarium.

Remember, each proactive step you take contributes to the well-being of your aquatic friends and the tranquility of your personal oasis.

And if you have additional advice for those looking to get rid of the bad smell from their fish tank, don’t hesitate to share it in the comments section below.

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