Why do my fish stay at the surface of the aquarium?

Are your fish staying at the surface of your aquarium and you are wondering if there is a problem? Naturally, aquarium fish move at different depths in the tank. Even if some varieties prefer to stay at the bottom, others will enjoy the middle or upper regions.

However, if you notice that your fish spend the majority of their time at the water's surface, this could indicate an underlying problem. Of course, it is also possible that your fish are just asking for food, as they are big gluttons.

A breathing problem

When fish stay near the surface, it means they are trying to breathe more easily. In fact, fish breathe thanks to their gills. The latter allow them to capture dissolved oxygen, without association with the H2O molecule. Dissolved oxygen levels are generally higher near the surface because there is an interaction between the water and the air.

There must be movement at the water's surface for air and water to be in contact, which will provide oxygen. Therefore, you need a filter that puts the water in motion at the surface of the aquarium, or an air pump that will increase the oxygen level in the water. There is also the solution of oxygenating plants that can be purchased in specialized stores.

> ⭐ Discover our range of air pumps for aquariums ⭐ <

When fish do not receive enough oxygen, they will try to compensate by moving closer to the surface. You might also observe a similar phenomenon when fish tend to stay near the bubbles from elements of your decor or rocks. Unless it is a surface fish, there is no reason for it to open its mouth to breathe outside of the water.

If this is the case, it means that there is clearly a lack of oxygen, which could be explained by injuries, parasites, or even certain diseases like flukes. But if the phenomenon is global—that is, if you have a group of fish exhibiting the same behavior—then it is a safe bet that the conditions of their habitat are not optimal.

Pay attention to water quality

To remedy this problem, you should start by performing a nitrite test, as well as a pH test of the water. You must study the possibility that you have a quality problem with a temperature that is not adapted, an incorrect pH level, too much ammonia, nitrates, or nitrites.

> ⭐ Find equipment for analyzing aquarium water here ⭐ <

Afterward, continue your investigations to understand why your aquarium is lacking oxygen. Your goal will be to improve the aquatic environment. If you ever have cloudy or polluted water, it could mean that you have poured in far too much food.

Also check that you do not have any dead fish in your aquarium and if so, remember to remove them. The same applies if you have rotting plants. Indeed, these are sources of bacteria that will harm the quality of life of your fish. In any case, do not forget to replace your aquarium water to achieve a healthy balance.

Always proceed with partial water changes, using conditioned water at the same temperature as that in the tank: a total replacement destabilizes beneficial bacteria and stresses the fish. To understand what your tests are measuring, read our article what are nitrites in an aquarium and our guide when should you change the water in an aquarium.

Consider the possibility of overcrowding

When you have an aquarium with too many fish, a natural pollution sets in, resulting in a low oxygen level. Moreover, bacteria can also develop more easily, but they will be sources of disease.

To avoid this phenomenon, it is important to respect the basic rule, which is 4 liters per adult fish with a size of 3 cm. This is a general characteristic, as once again there are disparities between species that tend to pollute or consume more oxygen.

This is an indicative rule for determining the size of the aquarium and the number of fish. But to refine this result, do not hesitate to do additional research. In parallel, also invest in oxygenating plant species and an aquarium bubbler.

To estimate the appropriate population for your volume, consult our article how many fish in an aquarium.

An aeration problem

It is important to have water in motion, as this allows for better quality water due to the movement of surface water with deep water. As a result, the fish benefit from a better supply of dissolved oxygen.

To achieve this, you cannot ignore quality filters that allow for the elimination of waste and also excess food. But you must check the filters regularly, as they can show certain defects or may need to be replaced.

To bring a more significant amount of oxygen into your aquarium, consider using bubble decorations such as an air stone.

Not only will you benefit from the many advantages of these elements, but you also add an extra decorative touch.

An air pump does not directly "push" oxygen into the water: it is mainly the bubbles that rise and agitate the surface that promote exchanges. To choose the right power, read our guide how to choose an air pump for an aquarium.

Water temperature that is not suitable for your fish

Water temperature also has its influence on oxygen concentration. Cold water contains more oxygen than warm water, so be vigilant in case of hot weather.

If you notice that the aquarium temperature is tending to rise, you must cool it down and, if necessary, move it if you have direct sunlight. In case of high temperatures for a long period, your fish risk not enjoying it because of a drop in dissolved oxygen.

During a heatwave, keep the aquarium away from direct sunlight, turn off the lighting during the hot hours, and increase surface agitation. Our detailed tips are gathered in the article how to cool down an aquarium.

Feeding aquarium fish

• Conditioning: Fish can be conditioned to associate the water surface with feeding. If you always feed them by throwing food at the surface, they may get used to gathering there in anticipation of food.
• Pavlovian response: Just like the dogs in Pavlov's experiments, fish can develop a conditioned response. When they see a person approaching the aquarium or notice other signs associated with mealtime, they may gather at the surface in anticipation.

Considerations on Feeding

• Type of Food: Some foods float on the surface, which can encourage fish to eat at the surface. On the other hand, foods that sink quickly will encourage them to look for their food in the lower layers of the aquarium.
• Frequency and Quantity: Overfeeding can cause fish to stay at the surface, especially if they expect to receive food often. It is important to follow a regular feeding schedule and not to overfeed your fish.

Health Effects

• Buoyancy Problems: Inappropriate feeding can lead to buoyancy problems in some fish. For example, a diet too rich in air (like certain types of flakes or pellets that float on the surface) can cause swim bladder problems.
• Water Quality: Overfeeding can also degrade water quality, increasing ammonia and nitrate levels, which can stress the fish and push them to seek oxygen at the surface.

In conclusion

When fish stay at the surface of the aquarium, it can be a sign of several potential problems, some of which can be dangerous to your fish's health. Here are the most common reasons:

1. Lack of Oxygen: This is the most common cause. If the aquarium water is not sufficiently oxygenated, fish come to the surface to access more oxygen. This can be due to inadequate filtration, overcrowding, or too high a water temperature (warm water holds less oxygen).

2. Poor Water Quality: High levels of nitrates, ammonia, or toxic chemicals in the water can stress the fish, pushing them to seek fresh air at the surface. Regular maintenance and water quality tests are essential.

3. Diseases: Certain health problems, such as respiratory tract infections or swim bladder diseases, can cause fish to stay at the surface.

4. Stress: Stress due to changes in the aquarium environment, such as new fish, lighting that is too intense, or loud noises, can also cause this behavior.

5. Feeding: Sometimes, fish come up to the surface waiting to be fed, especially if they have been conditioned to receive food in this manner.

Is it dangerous?

Yes, it can be dangerous. If fish stay constantly at the surface, it generally indicates a problem in the aquarium environment that must be resolved quickly to ensure their health and well-being. Here is what you can do:

• Check Water Quality: Use a test kit to check the levels of ammonia, nitrites, nitrates, and pH.
• Improve Oxygenation: Make sure your filtration system is working properly and consider adding an air pump or air diffuser to increase oxygenation.
• Check the Temperature: Check that the water temperature is appropriate for the species of fish you have.
• Reduce Stress: Minimize stress factors in the aquarium environment.
• Consult a Specialist: If the problem persists, it may be useful to consult a veterinarian specializing in fish or an experienced aquarist.

It is important to act quickly, as staying at the surface for a prolonged period can be harmful to fish and indicate environmental problems that must be solved to ensure the health of your aquarium's ecosystem.

Diagnosis and action plan

Before acting, take a minute to observe who is affected and at what time. The answer points directly to the right cause.

1. Increase surface agitation. Aim the filter outlet toward the surface or add a bubbler: it is the quickest way to bring up oxygen.
2. Measure the water. Nitrites, ammonia, pH, and temperature. A quick test is enough to spot a nitrite spike.
3. Do a partial water change. With conditioned water at the same temperature, if the tests are bad.
4. Lighten meals. Reduce the quantity and remove uneaten food.
5. Check the filter. Rinse the filter media in water taken from the aquarium, never under the tap, to preserve the bacteria.

If a fish shows signs of illness (spots, damaged fins, swelling), our aquarium bacteria range helps stabilize the water, but specialized advice remains preferable for treatment.

Frequently asked questions