Why Do Guppies Swim Up And Down? (Main Reasons)

Why Do Guppies Swim Up And Down? (Main Reasons)

Image of a guppy swimming up and down

Guppies usually swim up and down when they are stressed. Various issues like unfavorable living conditions, poor water or food quality, lack of space, the stress from being bullied, loneliness, or underlying diseases cause guppies to swim up and down the aquarium water, which isn’t normal.

Now, if you notice your guppy pacing for a long time, you should suspect that something is wrong. It’s wise to look for potential causes and fix them before they cause severe distress to your pet.

Reasons Why Guppies Swim Up And Down

Guppies are mostly top swimmers. This means they prefer to swim in the upper levels of their aquarium.

However, these fish don’t entirely restrict themselves to this area.

They will explore the rest of the tank whenever they want. It’s not normal for guppies to constantly swim up and down.

Given below are some of the main reasons why guppies swim up and down.

Unfavorable tank conditions.

Guppies are very sensitive to changes in their environment.

Common issues like changes in the water chemistry, water quality, or compatibility issues can cause stress to the fish and prompt them to swim up and down along the sides.

Poor water quality.

Guppies need a clean and hygienic environment with friendly tank mates. They cannot thrive in a poorly maintained tank.

If the tank is unclean, there will be toxins in the water. Toxins like ammonia and nitrates are invisible to the eye.

Although they don’t make the water look unclean, they are poisonous to guppies.

If there are toxins in the water, you should be able to fix the problem with a partial water change.

Toxins will also build up if your filter doesn’t operate efficiently. You may have to clean your filter and use fresh filter media.

Also, if you have added more fish to your tank, you may have to upgrade your filter to cope with the bio-load in your tank.

Water chemistry problems.

Guppies can tolerate slight changes in water pH and temperature.

However, sudden and severe fluctuations in water pH and temperature affect them adversely.

If you don’t regularly change the tank water or clean the filter, the water parameters will change over time.

It’s a good idea to test the water in the tank if your guppy starts pacing up and down.

It will help you identify the change in parameters and fix it without delay.

Overfeeding or insufficient feeding.

Guppies are very hungry fish. So they happily gobble up anything edible.

However, overfeeding is detrimental to their health. It leads to digestive concerns that create discomfort for the fish.

Guppies may behave unusually in such circumstances.

Insufficient feeding or poor-quality feed also causes similar issues.

If you don’t feed them properly, they will seek food in their surroundings.

While they will satisfy their hunger by eating anything within sight, it may not be the best option.

Consuming poor-quality food can trigger digestive problems.

It can also lead to pacing, which indicates that the fish is under stress.

Underlying diseases.

If your guppies are suffering from any illness, they may swim up and down.

You should check for illnesses if the water parameters are fine and the tank is clean, but your guppies continue to pace along the sides of the tank.

Inspect your guppies closely to identify any visible signs of diseases.

For example, discoloration of the fins or body, presence of patches, or any changes in appearance can signal a problem.

You should quarantine your guppies till you identify the problem.

Adding aquarium salt to the water will also help you tackle various parasites in the tank.


Guppies are friendly fish. They get along with most community fish.

However, they are very small fish and hence prone to attacks from bigger, aggressive tank mates.

A bullied guppy undergoes a lot of stress. As a result, it will display behavioral changes.

You may also notice signs of physical injury like tears or rips in their tails or fins that indicate they have been in a fight.

Observe the dynamics in the tank to assess whether other fish attack your guppy.

For example, aggressive fish like bettas and barbs may chase or nip it.

You may have to separate the two fish at least temporarily to control this problem.


Guppies get stressed when they don’t have enough space to swim.

They become unhappy when they cannot freely explore their surroundings or compete for resources.

Hence, guppies will not be comfortable in overcrowded tanks.

They resent not only the presence of too many tank mates but also too many tank decorations.

Anything that stifles their movement; stresses them out and causes them to act differently.

They may swim up and down along the sides of the tank if they face this problem.


Guppies are schooling fish. They live in large groups in the wild.

Hence, they are happiest when kept with their kind. Social interaction helps them stay active and healthy.

The lack of companionship can cause guppies to swim up and down.

Lonely guppies are often unhappy. They restrict themselves to one part of the tank.

If the population of guppies in your tank has dwindled, the ones that remain will undergo stress.

You can help them out by introducing more of their kind into the tank.

The ideal school size for guppies is six.

When you keep them in big groups, they will display schooling behavior and generally be very content.

Large groups of guppies will also make your tank look very lively and beautiful.

When Should You Worry About Guppies Swimming Up And Down?

It’s normal for guppies to occasionally swim up and down along the edges of the aquarium glass.

When they do it as a group, they are usually just enjoying the water and playing in the current.

In most cases, they stop after a while and resume normal activity.

It is also normal for guppies to surf along the glass when you introduce them to a new tank.

New fish take time to explore their environment and adjust slowly to the new setting.

Your guppies may temporarily display this behavior when you change the water.

Here, they are just trying to adjust to the changes in the environment.

Some owners observe that their guppies perform glass surfing when they are around.

In this case, the fish associate your presence with food and expect you to feed them.

In these cases, they usually limit this behavior to only when people are around.

The guppies will be busy with other activities for the rest of the time.

If you have an established tank and water parameters are under check, your guppies should not pace for more than a few minutes at a time.

However, if your guppies keep at it for several hours, you can suspect something is off and investigate the problem.

Begin by checking the water parameters of your tank.

From there, you can proceed to look for illnesses, incompatibility issues, and nutritional deficiencies.

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