As a fish keeper, you may wonder why your Corydoras are hiding and if there is a way to make your fish more active.

The hiding behavior is a common concern among corydoras keepers and results from several factors, most notably poor house conditions and stress.

This article will discuss seven reasons why your corydoras might be hiding and how to make them more active.

Photo by naturalhistoryman on Flickr

Normal cory catfish behavior

Corydoras are popular bottom fish in aquariums due to their peaceful nature and ability to keep the substrate aerated and free of food remains. Cory catfish are diurnal fish, tending to be more active during the day.

By night it’s normal for them to hide in places such as plants and decorations. However, during spawning cory catfish might be active at night.

During the day, as long as the fish are in adverse conditions, the Corydoras will swim and turn over the substrate in search of food. This habit is beneficial in most aquariums, as turning the substrate reduces the chance of oxygen-depleted zones. They are very lively fish and normally don’t hide a lot. 

This continuous exposure of all substrate layers to the water column is essential to maintain the activity of the bacteria present, consuming detritus, organic matter, and ammonia.

In nature, cory catfish live in schools that range, depending on the species, from 10 to sometimes more than 100 fish. In an aquarium, it means keeping at least six Corydoras together to ensure they feel safe and comfortable. When alone, Corydoras tend to be stressed and less active.

Cory cats are very peaceful and friendly fish and rarely get involved in fights with other fish, so they are perfect tank mates for many other fish.

Why do cory catfish hide?

If your cory catfish is hiding, there are a lot of possible causes for this problem. The most common causes are: stress due to bad tank conditions, other tank mates or your fish might need time to adjust to its new tank.

Here are the most common causes explained into detail.


Stress is the main reason why corydoras hide. Stress is a physiological response generated by some environmental issues, the most common being suboptimal water conditions for these fish.

Stress is responsible for lowering the fish’s immune response (it can’t fight off disease), and leaving the fish lethargic and with unusual behaviors.

Among the numerous factors called stressors, one of them is strong lighting. If your Corydoras are hiding more often than usual, ensure your aquarium lighting is adequate for your fish’s needs.

Adding floating plants to their tank also helps to block light.

Another common cause of stress in Corydoras is poor tank conditions. If your aquarium is not properly filtered and maintained, ammonia, nitrite, and nitrate levels can quickly build up, making your aquarium environment toxic to your fish. 

Make sure to perform regular water changes and keep the tank water quality within the proper levels for the species. 

Testing your water on a weekly basis is essential. This can be done using a test kit (check on Amazon)

Wrong tank mates

When choosing tank mates for corydoras, it’s essential to consider their friendly personalities. Corydoras are calm fish that are not aggressive toward other fish. Therefore, you should choose tank mates that are not large, aggressive, or territorial (unlike cichlids).

Related Read: Best Cory Catfish Tank Mates (Guide)

Some good tankmates for corydoras include other peaceful freshwater fish such as tetras, rasboras, and guppies. In addition, small invertebrates such as shrimp and snails are also excellent choices for tank mates.

Be careful when choosing tank mates that need very different water conditions. For example, some fish prefer more acidic water, while others prefer more alkaline water. Ensure all the fish in your aquarium can thrive in similar water conditions.

Overcrowding is also a common problem, especially in small aquariums. When we have fish in a small space, they can get stressed. 

Along with this, the water has more bioload produced by the fish, which helps to quickly degrade the quality of the water, further damaging the health and behavior of the fish.

Overcrowding can limit available space and leave fish stressed, disoriented, and with no hide. When fish feel threatened, they may seek refuge in plants, decorations, or other hiding places, but if the tank is too crowded, there may be few places to hide, increasing stress.

Your cory catfish is sick

Sick corydoras can hide for protection. Watch for signs of illness in your fish, such as lethargy, lack of appetite, or changes in appearance and behavior. If you suspect your corys are sick, consult a veterinarian or a fish specialist.

Read our cory catfish behavior article if you want to know whether the behavior of your cory catfish is normal.

Wild-caught fish

Wild Corydoras recently caught from nature may be more likely to feel shy, and scared and hide in the tank. 

Wild fish need time to adjust to their new environment and get used to humans. Be sure that your aquarium is ready to receive them, with ideal conditions for their needs, and that the fish are properly quarantined.

Some wild-caught fish never get comfortable in a tank and will stay shy, even after this period of adapting (which can take moths).

Adjusting time

Corydoras that have just been put into a new aquarium need time to acclimatize and feel comfortable in the new environment. Even captive-bred fish need time to adapt and get used to new environments. 

If you’ve just added new cory fish to your tank, it’s normal for them to hide and be shy for a while.

If you provide the right environment and ideal conditions for their needs, the fish will gradually adapt and feel more secure in your tank.

Filter that's too strong

Cory catfish usually like some flow in their tank. They will enjoy swimming against the current.

However, if the filter is too strong, it can create a stressful environment for the cory catfish. A strong water flow can lead to stress and physical exhaustion.  

Also, a strong filter can create a water current that makes it difficult for cory catfish to move. It is essential to ensure that the filter is adjusted to prevent this.

Having a lot of live plants in the tank also helps to create less turbulent zones.

Tips for making your cory catfish more active

To ensure that cory catfish will thrive and be active in the aquarium there are basic steps that will help you keep your fish healthy and active. 

These tips are often very easy to implement, but will create great results.

Water quality

Ensure that the aquarium environment is appropriate for the cory catfish. 

Keeping the aquarium clean and the water stable is paramount.

Always carry out partial water changes and periodically clean the filters and decorations, and siphon the substrate.

Make sure to research the preferred water parameters of each species, such as water temperature.

Hiding places

Cory fish are very active, so they need a spacious aquarium with decorations like driftwood and plants, forming hiding places.

Unlike what your intuition would say, having more hiding places will make your cory catfish less stressed and more prone to coming out.

Corydoras like to retreat to safe, secure places where they feel comfortable. 

Great hiding places are live plants, rocks, driftwood or caves.


Live plants, besides helping in water quality, are present in the natural environments of many corydoras and are a great way to provide additional cover for these fish.

In addition to plants placed directly on the substrate, you can also use floating plants such as Salvinia, which helps to create shaded areas in the aquarium, creating different environments where the fish can explore.

Using live (or artificial) plants can help reduce stress in corydoras and make them more active, with behavior closer to nature.

Dim lighting

The eyes of corydoras are sensitive; because of this, these animals suffer in conditions of intense light.

In nature, these animals occur mainly in areas shaded by forests. So keeping low lighting in the aquarium can make them more comfortable and active; this tip is mainly valid for newly arrived animals still adapting to the new aquarium.

LED lamps with dimmers are a good option for controlling lighting. Floating plants are also a great way to dim bright lighting.

Add schooling fish like tetras in the middle and upper layer

Tetras are schooling fish that like to swim in groups and are often used in aquariums to help other species feel more secure and comfortable. 

Bottom-dwelling fish look at other fish to avoid predators as they have worse vision.

Corydoras are an example of this, as they tend to become more active and move around more when is a group of fish swimming comfortably in the same tank.

You will note that schooling fish can help reduce stress and unusual behavior in some fish species, resulting in a healthier and more balanced environment for all aquarium inhabitants.

However, it is crucial to be careful when adding fish to your aquarium and to make sure that the amount of fish is adequate for the size of the tank and the specific needs of each species.

Feed them properly

Proper nutrition is essential for all animals. Cory catfish are omnivores and need a varied diet with live and dry food.

It is necessary to ensure that the diet is balanced and that the fish receive high-quality food, for this, you can use commercial food such as pellets and bottom pellets together with live or lyophilized food such as bloodworms, daphnia, and nauplii.

Make sure to read our full diet guide on the best foods for cory catfish.

Avoid external disturbances

When the aquarium is kept in places with constant passage of people, or many lights or noises, cory catfish can feel stressed, leading to behavior change and health problems. For your fish to stay active, try to avoid sudden movements, loud noises, and strong room lighting.

Observe your fish regularly

Observing your fish is the best way to know if all is well with them. A tip is to use the feeding time to see if all the cory catfish show up to eat and if they are healthy. If you notice anything amiss, take immediate action to correct the problem.

Keep them in a group

Cory catfish are social fish and need to live in groups to thrive. Be sure to keep at least six cory catfish together in your aquarium. This will help to avoid stress and ensure your fish are happy and healthy. Link to article

Research tank mates

When choosing aquarium mates for your cory catfish, it is important to select compatible species. Aggressive or territorial fish can stress and even attack cory catfish. Make sure to research the species before adding them to your aquarium.