Why Do Fish Lay On The Bottom Of The Tank?

Most aquarium owners will usually see their fish swimming in the middle or near the top of the water. When a fish is seen laying on the bottom of the tank, they will start to panic and wonder why.

Why do fish lay on the bottom of the tank?  It is usually due to stress, the fish are sleeping, unbalanced water parameters or they are bottom-dwelling fish species.

Above are usually the main cause for the fish to lay on the bottom of the fish tank, but other reasons could be as well. Most of it isn’t something to be concerned about, but those that are can be corrected easily. So let’s sink into it!

What Causes Fish To Lay On The Bottom Of Tank

There are many reasons why a fish can lay on the bottom of the tank. It could be stress internally or externally, rapid water temperature changes, they are sick, or just sleeping.

To find out why your fish are laying on the bottom of the tank, keep reading.

Stress Can Cause The Fish To Lay At The Bottom Of Tank

One of the reasons fish can be found laying on the bottom of the fish tank is due to stress. When they are stressed, the color will be a bit darker shade and they appear motionless on the bottom of the fish tank. Stress is caused by both external and internal sources.

External Sources Of Stress

  • Lighting: For any fish species, lighting is very important. In their natural habitat, there are daylight hours and nighttime hours. If you have an aquarium that has the lights on all day and night, the fish will begin to get stressed.  All species of fish do sleep and they need sleep to recover from their daily activities.  Depending on the species, some fish will sleep during the day and some fish will sleep during the night.
  • Pets:  If you have a pet in your homes such as a cat or a dog, they can cause stress for the fish. Fish are at the bottom of the food chain and they see a dog or a cat as predators. When the fish see them close-by, they will get stressed and natural instinct will tell them to go into hiding until the danger is gone.
  • Moving:  Whenever the fish is being moved around, they will get stressed. Whether moving the fish across the room to another tank or moving to another home, they are being exposed to a different environment. To help prevent the fish from getting stressed, you can use stress coat to help reduce stress in the fish.  
  • Loud Noises:  Fish are sensitive to noise and could cause them to be stressed. While fish cannot hear the noise, they can feel the vibrations from the noise. Sound travels four times faster in water than through air. This is why it’s never a good idea to tap on the glass of an aquarium. Other things such as televisions and sound systems can stress the fish due to the noise. Try to keep electronics such as television and sound system far from the aquarium.

Internal Sources Of Stress

  • Rapid Water Temperature Change:  Every time there is a change in the water temperature, especially a quick rise or drop, it will cause the fish to become stress.  When the water temperature goes up, the oxygen level will usually decrease and the fish will start to become stressed.  The same goes for when the temperature goes down too quickly, they are not able to cope with it and will cause them to become stress.
  • Wrong Tank mate:  A fish that doesn’t get along with other fish tend to get stressed. For example, Betta fish don’t get along with another male Betta. They will fight each other to death. If not, they will go into hiding. This kind of behavior will lead to the fish being stressed.  It’s best to remove one or the other so they won’t be stressed.
  • Fish Disease And Illness:  When a fish is sick, it will lay on the bottom of the fish tank motionless. They may sometimes hide under rocks and between plants. If you noticed that the fish is sick, it’s best to remove the fish out of the fish tank. Put them into a different tank and treat them with medication.
  • Overcrowding Fish Tank:  When a fish tank is overcrowded with fish, it will be hard for them to swim around.  Fish need some space to swim and move around. If the aquarium is too cramped with fish and they can’t swim without bumping into another fish, they will get stressed. This is the reason why most fish tank than is overcrowded will tend to see a lot of fish laying on the bottom of the fish tank.  The standard rule of figuring out the proper fish population for your aquarium is the four grams of fish per one liter of water rule.  Also, take into account how many aquarium decorations and plants you have.

The Fish Is Sleeping

Fish do sleep and they need to sleep every day. Surprisingly, fish require to sleep anywhere from eight to twelve hours of sleep each day. Some fish will sleep during the day, while others will sleep at night.

When fish sleep, most will lay on the bottom of the fish tank to sleep. Others may find a spot between rocks or plants to sleep.

It could be hard to tell if they are sleeping because fish don’t have eyelids. However, there are a few signs to look for when the fish is sleeping:

  • slow movement of the fin and tail: The fin and tail will sway back and forth slowly while the fish is sleeping.  They do this to move water into their mouth and gills to breathe.  Also, the movement of the fin and tail helps keep them in place while they sleep.
  • Slow movement of the mouth and gills:  For the fish to keep breathing oxygen while sleeping, they need to keep their mouth and gills moving. When the fish is sleeping, their gills and mouth will slowly open and close. This is enough for them to breathe while sleeping.

It’s important to know your fish habit so if you see them laying on the bottom of the fish tank, it should be a concern or not.

Bottom Dwelling Fish Species

why do fish lay on the bottom of fish tankIf the fish are laying on the bottom of the fish tank all the time, it could be because they are bottom dwellers or bottom feeders. These fish species will spend most of the time scavenging for food at the bottom of the fish tank.

Some of the popular bottom-dwelling fish includes:

  • Peppered Cory Catfish
  • Suckermouth Catfish
  • Zebra Loach
  • Twig catfish
  • Kuhli Loach
  • Bumblebee Goby
  • Yoyo Loach
  • Brittlenose Plecostomus
  • Siamese Algae Eater
  • Tiger Shovelnose Catfish
  • Dwarf Gourami
  • Otocinclus Catfish

Unbalanced Water Parameters

If the fish is laying at the bottom of the fish tank, it could be the water parameters are unbalanced. Fish are very sensitive to the unbalance of their water. Things from overcrowding to a clogged filter, a fish will become sluggish and motionless, spending their time laying on the bottom of the fish tank.

PH Levels

One factor that can affect the water parameters is pH balance. A significant change in pH balance can mean life and death for the fish, especially smaller and sick fish.

A fish tank with a pH between 5.5 and 7.5 is ideal for the fish to survive.

To prevent the death of the fish or other health issues, it’s always a good idea to monitor the pH balance of the water. It’s recommended to test the pH balance of the water twice a week to make sure the water pH balance is at its normal level.

There are a lot of things that can affect the pH balance in the fish tank. If you recently added new fish, live plants, or aquarium decorations, this can cause the pH balance to change. Also, adding chemical additives or treating the water with medications can change the pH balance of the water as well.

The above addition might not change the pH level a lot, but changing the water, cleaning the tank, or replacing the substrates of the fish tank will.
After any of these events, always test the water pH level. While it may register the pH level is normal, it might change in a couple of hours or a few days. Always check the pH level daily.

Also, if the pH level is out of its range, the fish will start to show signs of stress. They will begin to descend to the bottom of the fish tank and lay there.

If you noticed the fish is laying at the bottom of the fish tank instead of swimming, as usual, you’ll need to correct the pH level as soon as possible. A quick way to return the water’s pH level to normal is to add pH balancer treatment, which can be found on Amazon.

Ammonia Levels

Another factor that could create an unbalanced water parameter is ammonia. Ammonia poisoning is common in aquariums that are just being set up. This is due to a lot of fish being added, a filter that hasn’t had time to settle in, and bacteria and parasites recently died off from treatment.

Besides a new tank set up, ammonia poisoning also happens to an established fish tank. A clogged filter, overfeeding the fish, too many fish wastes are things that could create ammonia problems for the fish. When there is too much build-up of ammonia in the water, it will start poisoning the fish.

The standard acceptable level of ammonia in freshwater and saltwater aquarium is less than 1 ppm (part per million).

If a high level of ammonia is present in the water, the fish will lay on the bottom of the fish tank.  Also, you may see red streaks across the fish entire body. The gills will turn purple or red and they will be motionless.

If you notice the above symptoms, it’s recommended to test the water for a high level of ammonia. If your ammonia levels are above 1ppm, immediate action is needed.  If you don’t, the fish will suffer a slow death by ammonia poisoning from internal hemorrhaging.

To get the ammonia level back under 1ppm, reduce or stop feeding altogether for 2 days.  Don’t worry, fish can survive for up to 3 days without any food.

Also, do a water change of up to 50% and lower the pH level to below 7.0. This can be done with chemical treatment.

Nitrates Level

Nitrates usually occur in an established fish tank. This is due to overfeeding, excessive fish waste, adding too many fish to the aquarium, or improper cleaning.

The recommended level for nitrates should be 20 ml/l

If this level of nitrate rises above the recommended level, the fish will start to display symptoms. The fish will move sluggishly through the water with rapid gills movement. They will usually rest laying on the bottom of the fish tank motionless.

Unlike nitrites, a sudden drop or rise in nitrate levels can be deadly for the fish within twenty-four hours. For this reason, you need to take care of the issue right away.

To lower the level of nitrates, do multiple water changes of 5% each day. Consider using a special filtration media to remove nitrates. A product called Nitrate Reducing Media Pad is a filter element in helping remove nitrates, which is found on Amazon.

In addition to the above, reduce or stop feeding for a couple of days until the nitrate level is at its recommended level.

Nitrites Level

Nitrites are another factor that could cause an unbalanced water parameter in the fish tank. With nitrites, it usually rises when the ammonia level has recently risen.
Things that affect nitrites to rise are similar to those of ammonia. Overfeeding and excessive fish waste in the water causes the nitrites level to rise quickly.

The recommended level of nitrites is 0-.2mg/l

When the nitrites level is above the recommended amount, it will start causing fish issues. The fish will lay on the bottom of the fish tank and have a rapid gill movement. A high level of nitrites does not allow the fish to metabolize oxygen in the blood properly.  For this reason, the rapid movement of the gill is to try to increase oxygen intake into the blood.

Nitrites poisoning will take up to a week to kill the fish. During this time, the fish’s immune system will weaken, which will make the fish vulnerable to ice, bacterial infections, and fin rot.

To lower nitrite levels in the fish tank, you can do a 50% water change, add chlorine salt after the water change, and reduce or stop feeding for a couple of days.


Fish you used to see actively swimming around, but all of sudden, it’s laying on the bottom of the fish tank.  This can be an alarming thing to see and usually will cause you to freak out. While it usually is a problem with the fish, it could be fixed if caught early on.  Treat the fish with the correct medication and it will be back swimming happily in the fish tank again.

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