Why Do Tetras Swim At The Top Of The Tank? (6 Common Reasons)

Image of a tetra swimming at the top of the tank

Tetras are one of the most common fish found in aquariums. They are vibrant in color and easy to care for fish. But why do tetras swim at the top of the tank?

Tetras swim at the top of the tank due to inadequate dissolved oxygen in the tank water, poor water quality, overcrowding, incorrect water temperature, and swim bladder disorder. Tetras might also swim to the top at specific times of the day if they are used to receiving food from you at that time.

Let’s talk about this in detail now.

6 Common Reasons Why Tetras Swim At The Top Of The Tank And How To Stop Them

Usually, tetras are content to swim around and share the same space. So it can be pretty troubling to see a tetra not swimming around with the rest of its tank mates as it should. This usually indicates that something is wrong with the tetra.

Given below are some of the most common reasons why tetras swim at the top of the tank.

1. Reduced oxygen level.

Fish breathe dissolved oxygen from the water. Dissolved oxygen is more at the top of the tank because that’s where the gas exchange takes place between the water and the outside environment.

This is why tetras suffocating from the lack of oxygen will usually swim at the top of the water. At times, tetras can also swim near the bubbles in the water.

In any case, these behaviors indicate a reduced level of oxygen in the tank water. The reduced oxygen level can also cause hypoxia and make the tetras come to the surface for breathing. So test the aquarium water for oxygen level regularly.

The oxygen level of the water can reduce because of the following reasons:

  • Ammonia and nitrite levels have increased in the tank water.
  • Tank water has got polluted.
  • You are overfeeding the tetras.
  • There’s a dead tetra in the tank.
  • The surface area of the tank is small.

To increase the oxygen level of the tank water, do the following:

  • Perform 50% water change.
  • Ensure that the filter is working correctly.
  • Top up the aquarium water with filtered water.
  • Do not overfeed the tetras.
  • Immediately remove the dead tetra from the tank.
  • Use a lengthy and shallow tank instead of a tall and deep one.

Recommended Further Reading:

2. Poor water quality.

Poor quality water is another reason why the tetras might swim at the top of the water.

While it’s good to assume that your tank is in perfect condition because the water looks crystal clear, the truth is, it might be deadly for the tetras.

High levels of ammonia, nitrites, or nitrates, as well as imbalanced pH, hardiness, and salinity can make it difficult for tetras to breathe.

Water quality can degrade due to the following reasons:

  • The tank is new.
  • The tank is overpopulated.
  • Tetras are overfed.
  • A dead tetra was not removed from the tank.
  • The filter is blocked or switched off.
  • The filter media is old.
  • Beneficial bacteria got removed.

You can check the aquarium water regularly using a reliable ammonia and nitrite test kit or device. If there is any trace of these chemicals, you should treat the water immediately. You can also do a partial water change and use an ammonia neutralizing agent.

To further improve the water quality, you can reduce the number of tetras from the tank, not overfeed the tetras, immediately remove dead tetras from the tank, keep the filter in proper working condition, and add beneficial bacteria back to the tank.

3. Overcrowding.

An overcrowded aquarium can cause major problems. When there are too many tetras in a tank, the oxygen level drops drastically and often with deadly consequences.

The easiest way to make sure that this doesn’t happen is to stop overcrowding the tank if you notice the tetras having a hard time.

Starting out, it’s important not to use generic advice like “one gallon of water per inch of fish” when you are trying to figure out the ideal tank size. That’s because many fish require more space than others, and some fish can be more demanding on the tank’s resources than the others.

Always take these variables into consideration before deciding on the tank size. Also, do plenty of research and learn all you can from other experts.

Related Further Reading:

4. Incorrect water temperature.

Water temperature is an important factor to consider when keeping tetras. This is because water temperature regulates the amount of dissolved oxygen in the water and affects the activity of the tetras accordingly.

Warmer waters have a significantly lower dissolved oxygen concentration than cooler waters.

Less oxygen leads to suffocation, making the tetras come to the surface where the oxygen level is usually high.

In order to avoid undesirable water temperature in your aquarium, regularly check on the temperature using a thermometer. Also, keep a tab on the water temperature more frequently in the summer, and be sure that you maintain it between 75°F to 82°F, especially if your tank holds tropical fish like tetras.

A malfunctioning aquarium heater can also cause the water temperature to rise. So fix the aquarium heater immediately or get a new one to prevent your tetras from suffocating.

5. Swim bladder disorder.

Swim bladder disorder is a very common ailment that affects fish.

Tetras with swim bladder disorder have difficulty maintaining their buoyancy and will float to the top of the tank, swim upside down or sideways.

The most common cause for this disorder is constipation. However, it can also be caused by overfeeding.

To treat swim bladder disorder, you can feed green peas, oranges, etc., to your tetras.

6. Feeding memory.

Tetras, and fish in general, are clever little creatures.

Tetras that have been fed by their owners at a certain time throughout their life will remember to swim toward the top of the tank in anticipation of food.

This can be seen as cute and funny, but it’s also an indication that the tetras are hungry.

However, if they always stay at the top of the tank, then something is wrong with the tetras. They might be swimming to the top because of one of the reasons discussed above.

Interesting Further Reading:

Where Do Tetras Usually Swim In The Tank?

Usually, aquarium fish like to swim at different depths of the water.

However, different fish species like to swim in different places. Some prefer to stay at the bottom of the tank, while others like the middle or upper areas of the aquarium.

Tetras like to swim more in the middle of the tank. However, they may still go toward the bottom or top of the tank to find food.

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