Why is my Cory Catfish Swimming Crazy? {Glass Surfing}

My cory catfish swim against the glass frantically. I’m told water parameter issues are the most likely cause.

Could it also be because of stress or dissatisfaction with their environment?

This article will try to explain why is my cory catfish swimming crazy.

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Why Is My Cory Catfish Swimming Crazy?

Cory cats swimming all over the tank is a behavioral expression. One of the significant reasons why Cory cats swim all over tanks is because of stress. It can also mean the fish are not happy with their environment for one reason or the other.

You might see your cory cats doing the following:

  • Swimming All Over Tank
  • Cory Catfish Glass Surfing
  • Swimming Up and Down Tank
  • Swimming at Top Of Tank

Cory cats might not be happy in their environment for one reason or the other such as:

  • Overfeeding
  • Overcrowding in their tank
  • Poor water quality
  • Poor tank conditions

Cory Cats Swimming All Over Tank

Why Are My Cory Catfish Swimming Up and Down?

It is very common for a cory catfish to swim up and down in a tank, they usually do this because:

  • they can see themself in the reflection
  • they are trying to work out what the reflection is.
  • to get air/oxygen.
  • just for fun.
  • they are ready to breed and this is one way that they show it.

Why Are My Cory Catfish Swimming at the Top of My Tank?

If there is a lack of oxygen in your tank your cory catfish will sim to the top of your tank to the surface to breath.  There will also be more oxygen in the water at the top of the tank.

If your fish are constantly swimming at the top of your tank you will need to check the water conditions with a testing kit (Available on amazon) to make sure all conditions are within tollerance.

You should also add an air pump (Available on Amazon) to your aquarium to make sure the water has enough oxygen in it.

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What to Do When you Find Cory Cats Swimming All over the Tank?

Glass surfing is a term the most aquarists use to describe the occasion of fish swimming up and down in the tank. It is one of the behavioral ways Cory Cats express how they feel at a particular time.

Often, your Cory Cats swimming all over the tank isn’t something to worry about. In some instances, glass surfing is expected in Cory Cats.

Some of the instances that you can expect your Cory Cats to swim all over tank when you:

  • introduce them to a new environment.
  • finish performing a significant water change
  • are close to the tank, and the fish are expecting food
  • make a substantial change in the water parameter of the container.

However, if all these do not apply to your case, you can evaluate the tank parameters. You should ensure that all the tank parameters and conditions are suitable and favorable for your Cory Cats.

You can continue experimenting and evaluating to establish the reason for their behavior. While these last, the best thing to do is ensure that the tank conditions are favorable for the fish.

Why Do Corydoras Swim to the Surface?

The most important reason why corydoras swim to the surface is because:

  • they need to breathe.

This is what they do on normal occasions in the wild and also in tanks. They go up to the top with their mouths open to breathe at the surface.

If there isn’t enough dissolved oxygen in the water, you will notice your Cory catfish doing this more often. A corydora may swim to the surface too often:

  • as a sign of stress.

Darting to the surface, gasping for air or erratic swimming patterns indicate levels of stress caused by poor water conditions or discomfort from the fish itself. It can be due to low oxygen or stress from tankmates.

  • A group of five or more corridors together may keep things calm and serene.

Why Is My Cory Catfish Glass Surfing?

Glass surfing is indicative of aquarium life that feels stress. It looks like cory catfish are trying to find a way out of your tank because they are uncomfortable.

There are many reasons why are Cory catfish would be glass surfing including:

  • bad quality water
  • poor tank conditions
  • improper feeding
  • aggressive tankmates

Usually glass surfing from Cory catfish is also coupled with a few of the other symptoms of stress including:

  • refusal to eat
  • gasping at the surface
  • pale or whitish color
  • erratic swimming patterns
  • lethargy
  • white spots on the body
  • discolored gills

We hope your Cory catfish can become satisfied with its home and we recommend adding at least four to five of its own species to calm things down. Consider the tank conditions and water parameters first and foremost to make sure they are ideal for this specific type of aquatic life.

Why Are My Corydoras So Active?

Corydoras are usually calm and tranquil at the bottom of your tank. They enjoy shoaling as well when they are social in a group of five or more. Active corydoras within its own group would be a fun and welcoming behavior.

Negative activity would result in:

  • glass surfing 
  • frantic/erratic swimming patterns

An active cory catfish should also have a large appetite to enjoy eating anything that you are offering. They will also be doing a great job rummaging through the substrate.

It is up to you as the aquarist to judge whether or not the activity is positively displayed or negatively seen as a reaction to poor tank conditions, high water temperatures, aggressive tankmates and frantic swimming as the response.

How to Tell if Corydoras Are Happy

Happy corydoras are ones who eat regularly and keep to themselves without feeling any stress from tank conditions or tankmates.

However, if a cory catfish is on its own for a long period of time and completely motionless, it might be lonely. Add more corydora catfish together and you may see them uniquely dancing around in the tank.

They will stay together for most of their day and enjoy each other’s company. You might notice some of the following tendencies:

  • Energized
  • Animated
  • Dancing
  • Constantly hungry

If you noticed your Cory catfish glass surfing, swimming up and down, swimming erratically, lethargic or refusing to eat then it is quite obvious to tell that this fish is not happy.

Tank Conditions for Cory Cats

It is not challenging to keep Cory Cats in your aquarium. They are hardy and can cope with tank conditions that are not extreme. Also, importantly, the feeding demand for Cory Cats is not tasking.

  1. Cory Cats are bottom dwellers. Therefore, they love to have gravel or substrates at the base of their tanks. You can add about 2 inches of gravel to your Cory Cat tank.
  2. Also, Cory Cats are lovers of live plants. Including live plants in their tank will provide them with hiding places for them to rest. Likewise, other decorations offer space for the fish to explore; hence, it keeps them happy.
  3. The tank condition demands of Cory Cats are not extreme. They can even survive and thrive in an established tank. They often explore a considerable range of water conditions.
  4. Cory Cats prefer to live in an aquarium with a pH range of 7.0-7.8. They also thrive in tanks that are within the temperature range of 72-78°F. They can cope with parameters that fall within this range.

It would be best if you prevented the accumulation of toxic compounds in the fish tank. Ensure that you keep the nitrate and ammonia level of the tank at 0ppm. Likewise, avoid making a sudden change to the environmental conditions of the fish tank.

Behavior of Cory Cats

Cory Cats are the peaceful species of aquarium fish. They are certainly one of the most desirable species when it comes to temperament and aggressiveness. They are the most suitable beginner catfish option because it is easy to take care of them.

Cory cats are accommodating and endearing. Thus, they usually don’t have any problem living with other fish in a community tank. They don’t fight back, so don’t keep them with aggressive fish.

Cory Cats can cope with almost any non-aggressive species in their tank. Some of the suitable tank mates for Cory Cats include other Cory, Swordtails, Tetra, and Otocinclus Catfish. They can also cope with non-fish tank mates like different species of snails and shrimps.

You should avoid keeping your Cory Cats with certain species of fish such as:

  • Cichlids
  • Oscars
  • Texas
  • Jack Dempsey

These species can give your Cory Cats a tough time if you keep them together in the same tank.

However, it would be best if you did not mistake the calm behavior of Cory Cats for being boring. This species of fish are colorful and active; thus, making them a good species. They also exhibit specific amusing and funny movements that can add life to your tank.


Cory Cats offer a good option for beginners that are looking to introduce Catfish to their fish tank.  This species of catfish are not aggressive, hardy, and easy to care for. They also have a significant adaptive ability as long as the change is gradual.

However, Cory Cats can sometimes exhibit some funny movements like glass surfing. When this happens, the first thing you should do is check your tank parameters and ensure that the fish are not stressed.

Also, importantly, you should only keep Cory Cats with suitable tank mates. Keeping them with aggressive and rough species can make the environment uncomfortable for them.


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Hello, I'm Jason. I'm the guy behind HelpUsFish.com. I volunteer at my local fish shop and I created this site to offer tips and advice on the fish I care for.