Why Does My Aquarium Stink?

by Aquarium Scoop | Last Updated: October 27, 2022

Having trouble with a smelly fish tank? Fish tanks smell bad for many reasons, but fixing the issue is usually pretty simple.

In this guide you’ll learn:

  • What makes a fish tank smell bad?
  • How to fix a smelly tank
  • Preventing future odors

The most common cause of a smelly fish tank is overfeeding. Fish overfed produce more waste than the filter can remove, causing a foul odor. This waste decomposes and releases ammonia, a toxic gas harmful to your fish at high levels.

Since ammonia can cause health problems for fish and contribute to the foul odor in your aquarium, if you think your fish are being overfed, try cutting back on the amount of food you’re giving them. You can also try feeding them smaller meals frequently versus larger meals occasionally.

Another common cause of a smelly aquarium is a dirty filter. Unfortunately, a dirty filter can’t remove all the waste and toxins from the water, which can cause foul-smelling water.

Follow the manufacturer’s instructions to clean your filter, or visit an aquarium store for help. You may need to clean it more often if you have a lot of fish or if your fish produce lots of waste. If your aquarium still smells terrible after cleaning the filter, the problem may be with the water itself, so a complete tank change may be a good idea.

5 Reasons Why Your Aquarium Might Stink

Like most aquarium owners, you probably don’t want your aquarium to stink. But sometimes, it happens. There are a few possible reasons why your aquarium might stink, and luckily, there are also a few things you can do to fix the problem. 

Dirty tank filter

Check your filter to ensure it’s clean and functioning correctly. A dirty filter can cause a build-up of toxins in the water, leading to a bad smell. We see this all the time at Aquarium Scoop.


If your filter is clean, the next most likely culprit is overfeeding.

When fish food decomposes, it releases ammonia into the water, which can cause a nasty smell. Too much food can also build up harmful toxins in the water.

Overcrowded tank

One possible reason your aquarium might stink is that you have too many fish. When there are too many fish in an aquarium, the water can become polluted and start to stink. If you think this might be the problem, try doing a partial water change and see if that helps.

Algae overgrowth

Another possible reason your aquarium might stink is that you have too much algae. Algae can release a musty smell into the water, and if there’s too much of it, it can make your aquarium stink.

To get rid of the algae, you can try using an algae eater or some algae-killing chemicals. However, if you’ve tried all of these things and your aquarium still smells, it might be time to call a professional. They can help you determine the problem and get your aquarium smelling fresh and clean again.

Expert Tip 🧠

If your aquarium smells stinky, it could be due to too many fish, too much algae, or something else. Try doing a partial water change or using an algae eater to see if that helps. If not, call a professional.

Live aquarium plants

Lastly, if you have live plants in your aquarium, they may be the cause of the smell. This is because plants release oxygen into the water, but they also release carbon dioxide.

If the water in your aquarium is too high in carbon dioxide, it can cause a bad odor. If you’re noticing a foul smell coming from your aquarium, don’t despair, there are a few simple steps you can take to eliminate the problem.

📚 Read More >> Aquarium Plants Turning Brown?

How to Fix a Smelly Aquarium

If your aquarium smells bad, there are a few solutions you can try to get your tank smelling fresh again.

Feed your fish less frequently and remove uneaten food

The first solution is to simply feed your fish less. Overfeeding is the most common cause of a smelly aquarium, so this is often the easiest fix. Just cut back on the amount of food you’re giving your fish, and be sure to remove any uneaten food from the aquarium. Old or uneaten food will start to rot and cause an unpleasant odor.

Buy a higher-quality filter

If your aquarium doesn’t have a good filter, or if the filter isn’t working properly, waste and debris can build up in the water, making it dirty and smelly. A quality filter will help to keep the water clean and clear. The Fluval/AquaClear HOB filters are a great option. While they do cost more than others, they will last forever if maintained. 

Reduce the amount of fish in your tank 

This is the hardest option because we know you love your fish, but if you have too many fish in your aquarium, you may need to remove some. Having too many fish in an aquarium can lead to high ammonia levels, which can be toxic to your fish. If you have too many fish, it’s best to remove some of them and give them to a friend. 

Important 🚨

Ammonia levels above 0.25ppm is extremely toxic to your fish and could cause death.

Make sure you’re cleaning your tank regularly. This means doing a full clean every few weeks and doing a spot clean (removing any visible debris) every week. It’s also essential to vacuum the gravel to remove any built-up waste. Ammonia and nitrites can build up over time and cause a foul smell. Test your water regularly and do a water change if necessary.

📚 Read More >> How To Clean Acrylic Fish Tank

Tips for Keeping Your Aquarium Fresh

We all know the feeling – you walk into your home and are immediately greeted by an unpleasant odor. After searching high and low, you finally realize the source of the smell is coming from your aquarium. If you’re here, you’re wondering how to fix the issue so your aquarium doesn’t stink.

Add live plants

Not only will they help to filter the water, but they’ll also add oxygen which will help to keep your fish healthy.

Keep the lid on

This will help to prevent evaporation and will also help to keep any unwanted smells out.

Expert Tip 🧠

A dirty filter is one of the most common reasons for an aquarium to start smelling. To avoid this, clean your filter regularly according to the manufacturer’s instructions.


If your aquarium still smells bad after taking these steps, the problem may be with the water itself. Ammonia and other toxins can build up in the water over time, making it necessary to do a partial or complete water change.

This will help remove any built-up toxins and waste from the water, improving its quality and smell.