Smelly aquarium, what to do?

What should you do if your aquarium smells? If your aquarium gives off a foul odor, you are probably looking for a solution to this problem. If an aquarium smells bad, there is always a reason. There are several possible causes.

Possible causes of the problem:

• Nitrite levels too high (which may be related to having too many fish).
  
  
• A population too large for the aquarium's volume.
  
  
• A filter problem or insufficient filtration.
  
  
• A lack of oxygenation.
  
  
• Stagnant water.
  
  
• A dead animal or plant.
  
  
• Poor substrate in the aquarium.

Each of these causes can stem from different issues.

Identify the odor to find the cause

The type of odor often gives a good clue as to its origin. Before touching the filter or emptying the aquarium, take the time to smell the water and observe the tank: this will prevent you from treating the wrong problem.

Nitrite levels too high:

Nitrite levels can be tested using different water testers: generally liquid drop tests (which are more accurate) or test strips. We offer several options from the JBL brand on our website:

=> Discover our guide to water quality testers.

If the test reveals that nitrite levels are too high, this may be due to several issues that you can generally improve without the help of any products.

If you have too many fish in your aquarium, nitrite levels and the fish's comfort will be severely affected. It is therefore advisable to regulate or reduce the number of fish as needed.(If you are unsure about the proper number of fish in your pond, do not hesitate to consult a specialist).

Too much food due to overfeeding or excessive portions can also lead to high nitrite levels because of the waste left by the excess food decomposing in the aquarium.

A lack of plants could also explain the high nitrite levels.
It is therefore preferable to add a certain number of plants proportional to the size of the aquarium and the animal species present. But you should not add just any plant; do not hesitate to find out which plant species would be suitable for your aquarium and the species that inhabit it. Dead plants also cause bad odors, so remove them as quickly as possible.

Finally, a lack of beneficial bacteria is one of the main reasons for nitrite levels that are far too high. Do not forget to seed your filter with bacteria that will help remove organic waste and prevent nitrite levels from rising. It is therefore quite important to maintain a large enough population of bacteria in your pond.

Warning! High nitrite levels can also cause mortality in the aquarium. It is therefore all the more important to check them and adjust them as needed quite regularly.

If the test reveals high nitrite levels and the fish show signs of distress, follow our emergency nitrite protocol.

Overcrowded aquarium:

Depending on the species you have in your aquarium, whether fish, turtles, or other animals, the aquarium population should not be too large. Regardless of the species, overcrowding is not recommended, as it will affect the water quality and the well-being of the various animals in the aquarium.

This is especially true because there will not be enough space for the animals' well-being, and the amount of waste will be far too high, inevitably causing foul odors in the aquarium. Furthermore, more animals mean more food, which can lead to more decomposing food and a higher risk of nitrite levels becoming too high.

Your filtration system may also no longer be sufficient to prevent the water from becoming cloudy.

Filtration problem or insufficient filtration:

If you do not have a filtration system in your aquarium, it is advisable to add one to filter the water, keep it at the best possible quality, filter out waste, and allow bacteria (mentioned above) to establish themselves.

If you have a filtration system, but the odor persists and you suspect the filter is the cause, it may not be powerful or efficient enough for your aquarium or the population inside it. It is therefore better to check whether the model you are using is sufficient for your needs.

It may also simply be that the filter is not clean enough. This could be due to a clogged filter, either because there is too much to filter or because it is not cleaned often enough. (Or, once again, the filter's efficiency is insufficient, so it would need to be replaced or cleaned very often, which is not a viable long-term solution).

Lack ofoxygenation:

A lack of oxygenation could also cause a bad odor in the aquarium. In fact, a lack of oxygen can cause the water to become cloudy due to the proliferation of harmful bacteria.

Furthermore, a lack of oxygen is bad for both the animals and plants in the aquarium. Oxygen is vital for the life and well-being of both.
A severe lack of oxygen can also cause health problems or even death.

To compensate for the lack of oxygen, it is advisable to add a few oxygenating plants to your aquarium, which will also provide hiding places for the aquarium inhabitants and supply some of the oxygen needed for their well-being.

But the most effective source of oxygen in the aquarium remains an oxygen pump (also called an air pump), which provides far more oxygen than plants and allows oxygen to be supplied in all circumstances.

=> To find out which air pump to use for your aquarium, do not hesitate to consult our guide on the subject.

Stagnant water:

Stagnant water can be a fairly common cause of a bad odor, and this usually happens due to a lack of water movement, which can be addressed using a water pump and an air pump.

Or due to their poor placement. You should also check that they are working properly and make sure they do not become clogged.
If you do not know where to place your pump in the aquarium, we have a short article on the subject: where to place an aquarium pump.

In addition to these two devices, which will create movement in the water, it is advisable to regularly change some of the water in the pond. About 20 to 25% of the water each week with fresh water. But this may vary depending on the needs and the animals present in the aquarium.

If you think the source of the odor is a lack of water changes and you want to address it, do not hesitate to read our guide to water changes.

A dead animal or plant:
Unfortunately, an individual may die in your aquarium, and regardless of the cause of death, it may be decomposing in a corner. This would cause waste and a strong odor in the aquarium; usually, you just need to remove it for the odor to disappear on its own after a while.

If you have a few small individuals and one of them has disappeared, do not hesitate to look in every corner, hiding place, or decoration, as it may have died out of sight and caused an unpleasant odor without you noticing its disappearance.

If you have plants in your aquarium, leaves or the plant itself may also die, which also causes an unpleasant odor. If this is the case, you can either cut off the dead leaves of the plant to make the odor go away, or if the entire plant is dead, you should also remove it and possibly replace it to avoid creating a gap or lack in the pond, depending on the purpose of the dead plant.

Some animal species will gladly get rid of dead plant leaves for you without you having to intervene.

Poor substrate in the aquarium:

Not all substrates are good for the aquarium. Some types of sand or gravel compact over time, and the waste trapped inside can eventually give off odors in the aquarium. It is important to choose your substrate carefully to avoid ending up with this kind of problem in the long term.

There are different types of recommended substrates depending on the species present in your aquarium. Do not hesitate to ask your specialized retailer for advice.

And this concludes the main causes of bad odors in aquariums. If none of the reasons mentioned above seem to be the cause of the odor in your aquarium, do not hesitate to contact a specialist on the subject.

Action plan: what to do today?

When the odor is strong, proceed in this order. Each step addresses one cause without creating a new one.

1. Look for the visible source: missing fish, dead snail, decomposing leaves, food scraps. Remove them.
2. Test the water (nitrites, and ammonium if possible) to see if the biological filtration is outdated.
4. Change some of the water with conditioned water at the same temperature, without emptying the tank. Our guide how to change the water in an aquarium details the method.
5. Siphon the substrate to remove accumulated waste.
6. Rinse the filter sponges in the water removed from the aquarium, if they are clogged.
7. Reduce feeding for a few days: an amount that the fish consume in a few minutes is enough.
8. Restart the bacteria if nitrite levels remain high, and check the water in the following days.

Prevent bad odors from returning

• Feed small amounts and remove uneaten leftovers.
• Perform regular partial water changes rather than infrequent major cleanings.
• Maintain the filter gradually, never cleaning everything on the same day.
• Monitor nitrite levels regularly, especially after adding new fish. Our guide which test kit to choose helps you get the right equipment.
• Count your fish from time to time and check hiding places.
• Remove damaged plant leaves before they rot.

Frequently Asked Questions About Bad Aquarium Odors