12 Reasons You See Fish Huddled Together in the Corner of the Tank

Most aquarium fish love swimming around and exploring their environment.

Fish species like bettas and fancy goldfish put on quite a show with their bright colors and flowy fins.

But what does it mean when you see fish huddled together in the corner of the tank?

1. Improper Water Temperatures

water temperature huddle fish

Understanding the optimal temperature needs of your fish is crucial for their health.

Tropical fish like bettas need warmer water temperatures ranging from 78-80° degrees Fahrenheit (25.5-27° C).

Cold-water fish species like fancy goldfish prefer lower temperatures between 65-72° degrees Fahrenheit (22° C).

If temperatures are too warm for your fish, they may stay near the bottom of the tank, where the water is cooler.

An increase in water temperature also causes a drop in oxygen levels. Without enough oxygen in the water, your fish will struggle to breathe.

When the water is too cold, your fish may huddle together in the corner of the tank near the heater.

Ambient room temperatures are usually not warm enough for warm-water species like betta fish and dwarf gouramis.

Maintain comfortable water temperatures with an aquarium heater rated for the size of your tank. The correct heater output is 3-5 watts per gallon of water.

Placing the heater near the filter allows for better circulation of the heat. This prevents uneven tank temperatures.

You must also keep your aquarium away from sunny windows or air vents to avoid sudden temperature changes.

Use a separate thermometer for checking temperatures. Built-in heater thermostats are not always correct and may fail.

Checking the water temperatures in several areas of the tank ensures no hot or cold spots.

Once you achieve ideal tank temperatures, your fish will swim around again.

2. Poor Water Quality

Aquarium fish are sensitive to toxins like ammonia and nitrite.

These toxins build up in the water from fish waste, uneaten food, and other decaying organic matter.

Poor water conditions cause stress and illness in your fish. Exposure to high ammonia levels can kill fish in a short period.

Fish suffering from ammonia or nitrite poisoning may stay in one corner of the tank, usually near the filter.

Some fish, like bettas, have a labyrinth organ to breathe fresh air. A betta with ammonia poisoning will stay near the surface and gasp for air.

Maintain favorable conditions in your tank with weekly cleaning and partial water changes.

A proper filtration system and live plants also help keep the tank clean by removing some of the harmful toxins.

Regularly testing your water parameters lets you get ahead of water quality issues before they worsen.

3. Stress From Other Fish

When you have a community tank, you must ensure your fish get along well.

Bullying and aggressive behavior cause stress in your fish. The fish getting picked on are more likely to spend much time hiding in the corner of the tank.

Schooling fish, like tetras and rasboras, feel safer in large groups.

Bettas prefer a solitary lifestyle and may become aggressive toward other fish. But, with the right tank mates and plenty of space, betta fish can do well in a community tank.

Research compatible fish species and ensure they can live in the same aquarium before setting up a community tank.

If you notice certain fish hiding in the corner most of the time, they are likely getting bullied.

Any time you see aggressive behavior in your community tank, you must take action right away.

Getting a larger tank or providing more hiding spots may solve the problem.

If the bullying continues, you may need to take more drastic measures. This involves moving the aggressive fish to a separate tank.

4. The Tank Is Too Small

small fish tank

Your fish need plenty of space for swimming and exploring.

A lack of space will cause your fish to become stressed. This stress results in lowered activity levels, and your fish may stay in one area of the tank for long periods.

Ensure your tank size is appropriate for the type of fish you have.

Inexperienced fish keepers often place bettas in small bowls because they believe the fish does not need a lot of space.

In reality, bettas need at least a 5-gallon tank to stay healthy and thrive. This is also the smallest-sized tank for creating a nitrogen cycle.

The nitrogen cycle supports fish health by converting toxins like ammonia and nitrite into less harmful substances.

Overcrowding is also an issue in community tanks. Too many fish in a tank causes stress and increases the chance of aggressive behavior.

More fish also equals more waste and debris, causing poor tank conditions.

The general rule of thumb is one inch of fish per gallon of water. Keep this in mind when you consider adding new tank mates.

5. Improper Lighting

The type of lighting in your aquarium affects the behavior of your fish. You must also consider the lighting needs of your aquatic plants.

Fish like bettas and goldfish prefer medium lighting. Bottom dwellers, such as loaches and catfish, need dimmer lighting.

When the light is too bright for your fish, they become stressed and may hide in darker corners of the tank.

Bright lights also cause excess algae growth in a fish tank.

Neutral white LED lighting is the best choice for your fish and live plants.

LED lights do not produce a lot of heat like incandescent lights. Many aquarium LED lights are adjustable as well.

Fish need a stable light cycle with around 12 hours on and 12 hours off. This light cycle helps support a fish’s circadian rhythm so they know when to eat or sleep.

Always turn your aquarium lights off at night so your fish can rest.

6. Your Fish Are Hungry

If your fish huddle in the corner of the tank, consider the last time you fed them.

When hungry, fish may conserve energy by huddling together or staying in one spot.

Ensure your fish get enough food at each meal without overfeeding them.

Some fish, like bettas, are greedy eaters. This usually leads to issues with overeating, such as bloating or constipation.

Bloating and constipation can lead to serious health problems like swim bladder disease or dropsy.

Instead of one large meal per day, feed your fish smaller meals twice per day.

Space the meals 6-8 hours apart. This allows for healthy digestion and helps prevent bloating and constipation.

Ensure the fish in a community tank are not having their food stolen by more aggressive fish. You may avoid this behavior by feeding different fish species on separate ends of the tank.

7. The Water Flow Is Too Strong

strong water flow

Bettas and fancy goldfish have difficulty swimming in strong currents because of their flowy fins.

If the filter is too strong, your fish will avoid swimming in the heavy water flow and stay in one place.

Choose an adjustable flow rate filter and put it on the lowest setting if your fish struggle with swimming.

You may also add a filter sponge to the filter nozzle to slow down the flow speed.

8. Your Fish Are Breeding

Female fish may hide in the corner of the tank when breeding because they feel more vulnerable.

Your fish will stay in one area until she gets ready to lay her eggs.

If your female fish has a swollen abdomen and there is a white spot near her vent, she is likely carrying eggs.

The female may refuse food as she gets closer to egg-laying and will stay in a quiet corner of the tank.

Once she lays her eggs, she will resume normal eating and swimming behaviors.

9. Not Enough Hiding Places

Too much open space and a lack of hiding spots make fish feel insecure.

Your fish may spend a lot of time in the corners of the tank or hide behind the filter.

Providing lots of hiding places for your fish gives them somewhere to go when they feel scared.

There is a variety of options for hiding spots, including:

  • Live/fake aquatic plants
  • Driftwood
  • Smooth rocks
  • Coconut caves

Live plants create a more natural environment for your fish and make them feel more comfortable. Another benefit of live plants is they also oxygenate the water and filter harmful substances.

Amazon sword, anubias, and Java fern are all excellent plant choices. These plants are low-maintenance and provide good coverage for your fish tank.

Floating plants like Amazon frogbit and hornwort provide shade for your fish. Be sure the floating plants do not block light from reaching other plants below.

Artificial plants are a good option as long as they are not made of plastic. Plastic plants have sharp edges, which may injure fish with delicate fins like bettas.

Instead, choose artificial plants made from silk.

Driftwood, smooth rocks, and coconut caves provide natural hiding spots for your fish.

Avoid tank decorations with sharp edges or coarse surfaces.

Do not place objects too close to the sides of the tank, or your fish might get stuck between them.

10. Illness

sick fish huddle together

Sick fish may hide in the corner of the tank because they feel more vulnerable to attack.

Check your fish for common signs of illness, such as:

  • Lethargy
  • Loss of appetite
  • Erratic swimming patterns
  • Clamped fins
  • Excess body mucus

Individual symptoms vary according to the illness.

If your fish is hiding and you notice signs of illness, consult your veterinarian immediately.

You may need to move your fish to a separate quarantine tank for treatment.

A quarantine tank is especially important if you have your fish in a community tank. Some diseases can spread to other fish in a short period.

Certain fish medications also cause damage to the live plants and beneficial bacteria in your tank.

Once your fish recovers from the illness, the hiding behavior should stop, and it will resume normal activities.

Check out our list of the most common betta diseases and what to do about them.

11. Sudden Environmental Changes

Sudden pH, temperature, or other water parameter changes can make your fish uncomfortable and stressed. These changes may cause your fish to stay in one area of the tank.

Temperature fluctuations are hazardous, as this can lead to temperature shock. To avoid this and for emergencies, read how to keep bettas warm without a heater.

Always maintain a stable environment for your fish. Do this by testing your water for toxins and performing weekly partial water changes.

Check the temperature of your tank with a separate thermometer to ensure your heater is working.

Besides changes within the aquarium, external environmental changes can also cause hiding behaviors in your fish.

Loud noises or sudden movements near your fish tank can scare your fish into hiding.

Provide your fish with a peaceful space by placing the aquarium in a quiet area of your home.

Avoid further stress on your fish by keeping other pets away from your aquarium, like cats and dogs.

12. New to the Tank

It is not uncommon for fish to hide in the corner of their new tank after you bring them home.

Your fish may hide for several weeks until it gets comfortable with its new environment.

Make your fish feel as secure as possible during this time.

Keep the tank clean and maintain a consistent feeding schedule.

Avoid loud noises or sudden movements, as this can startle your fish.

If you add a fish to your community tank, watch for signs of bullying or aggression.

Provide your fish with plenty of live plants and hiding places for comfort and security.

Once your fish becomes acclimated to its new home, it will stop hiding.

When Your Fish Play Hide-and-Seek

Seeing your fish huddled in the corner of the tank may be alarming.

But, there is usually a simple solution to this issue.

Explore possible issues with your tank setup and check your fish for symptoms of illness. If you have a community tank, watch for signs of bullying.

For new fish, give them time to get used to their surroundings.

Providing your fish with a comfortable environment makes them feel more secure and encourages exploration.

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Toni Tedescucci is a freelance writer who loves all animals, especially betta fish. When she isn’t busy writing for Betta Fish Bay, she’s spending time with her family or getting cozy with her cats and a good book.

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