Fish Laying at the Bottom of Tank; Should You Really be Worried?

Carol M.
Fisheries Consultant

Are you starring at your fish and wondering, "why is my fish at the bottom of the tank? " There are several reasons leading to this behavior. This behavior is worrisome, and depending on the factors causing it, it may be normal or a sign of trouble. Therefore, let's find out why fish lay at the bottom of the tank and learn how to handle them.

Reasons Why Fish Lay at the Bottom of the Tank

Understanding your fish behavior helps you determine which action to take. The following are the most common reasons fish will lay at the bottom of the tank.

  1. Fish Sleeping/ Resting

Your fish needs rest just like any other animal. These creatures follow general sleep rhythm patterns like humans. Fish love sleeping at night and being active during the day. Sometimes they may fail to get enough sleep at night; thus, they find some time to sleep during the day.

Some fish may cuddle up in nooks, rest on a substrate or sleep on plant leaves. This behavior is typical in bettas as they try to find unique spots. If your fish keeps sleeping a lot during the day, try to make some adjustments. 

Ensure you leave your fish in a quiet, dark area at night for them to get enough sleep. Massachusetts Institute of Technology also suggested that if you have a tall aquarium, consider making high towers of caves for the fish to hide and sleep, and they will start staying in upper waters.

  1. Your Fish is a Bottom Dweller

Some fish species are naturally adapted to live at the bottom for survival and hunting techniques. Some  examples are;
      • Clown loaches prey on snails
      • Kuhli loaches burrow their wormlike bodies in gravel
      • Zebrafish enjoy hiding out in the plants along the bottom
      • Corydoras stay at the bottom to scavenge
However, according to the Virginia Institute of Marine Science, most aquarium species will keep hovering along the bottom, so it's best to have a more horizontally extended tank than a taller one. So, if you find your fish mouth located more at the bottom of its head, it’s likely a bottom feeder. Some examples of bottom dwellers are as follows;
    • Chinese Algae Eaters
    • Kuhli Loaches
    • Corydoras Catfish
    • Otocinclus
    • Plecstomus
    • Synodontis Catfish
    • Zebra Loach
    • Twig Catfish
    • Bumblee Goby
    • Siamese Algae Eater
Image: Corydoras Catfish
Corydoras catfish lying on the bottom of tank
Source : iStock Photos
  1. Fish Diseases and Injuries

Your fish may be experiencing physical pain if it has injuries, and this will make it lay at the bottom due to lack of energy to swim. Also, some diseases can affect your fish and make it rest at the bottom—for instance, bacterial infection, parasitic worms, bladder disorder, dropsy or bet spine. If you notice any cuts, lesions, or spots, they may show that your fish is sick. The most common aquarium disease that makes fish lay at the bottom is ich, caused by  Ichthyophthirius multifiliis.   The disease presents white itchy spots, and the fish try to rub on rocks, gravel, and other features in the tank. So, it’s best to consult a veterinary officer to check on your fish and treat them.

  1. Unbalanced Water Quality Parameters

Water quality is critical for the survival of any aquarium fish. If you compromise quality, the fish will present some behaviors, causing stress and even death. Some of the water quality parameters that may cause fish to lay at the bottom include;

    • Ammonia Poisoning

Ammonia is a waste product that fish produces in an aquarium and can be lethal in fish. If the compound is in excess, it causes burns in gills and later death. Signs of ammonia poisoning are reddish/ purplish gills, red streaks on the body, and low appetite.

Fish suffering from ammonia poisoning will become severely sick and lay at the bottom. If you fail to intervene in any way, your fish dies from internal hemorrhage. Remember to maintain ammonia levels at 1ppm and avoid crowding in your tank.

If above 1ppm, you need immediate intervention

      • Reduce feeding
      • Lower pH to below 7
      • Change water up to 50%
      • Chemical treatment of water
    • Nitrate Poisoning

Continuous exposure to high nitrate levels in your fish makes them lose energy, become sick, and lie at the bottom. Nitrate is a compound of waste production in fish. Bacteria present in water convert the ammonia to nitrite then to nitrate.

Though the compound is less harmful than ammonia, it affects your fish slowly and causes death. Your fish will have faded colors, rapid gill movements, panting, low appetite, and lethargy. Therefore, maintain the tank nitrate levels at 10ppm. You can achieve this by reducing feeding frequency, adding air stones, avoiding overcrowding, and using filtration media. As an aquarist, there are cycling processes to follow and test the compound at least once a week to keep it in check.

    • High Water Temperatures

Temperature shock is a real threat to your fish. Though the fish enjoy warm waters, excess heat will make your fish have health issues. Hot water isn’t an issue, but oxygen availability. Warm water usually has low oxygen levels stressing out the fish.

Your fish will thus swim at the bottom where water is relatively colder; warm water will rise, leaving cold and oxygenated water at the bottom. Therefore, to ensure the survival of your fish, maintain the appropriate water temperatures to have the best level of dissolved oxygen, above 7.0 mg/L

    • Too Cold Water

Coldwater beyond the fish comfort range can cause trouble. Your tank water temperatures shouldn't be below 74 degrees F. Low water temperatures slow down the fish metabolic rate. Your fish are cold-blooded; that is, they can't regulate their internal body temperature with water temperature changes. 

Thus, too cold water harms your fish. With low metabolism, the fish becomes sluggish and sleepy. If this situation becomes a trend, your fish develop stress and will likely lie at the bottom of the tank.

    • PH Levels

The best pH levels for your fish are between 5.5 – 7.5 for it to thrive in the tank. An extreme change in the pH is very harmful to your fish, especially the young or sick, and can cause death. So, it’s best to test your pH levels at least twice a week for monitoring.

  1. Tank is Small

If you keep your fish in a small tank, you will limit their space for exercises and room for exploration. Fish in a small tank easily gets bored and lays on the bottom. Again, a small tank means more territorial aggression among the fish. Thus, the timid members will quietly lay at the bottom of the tank to escape the fights. Therefore, have a bigger tank for your fish, and they will become less temperamental.

  1. Fish is New to the Environment

Fish in a new tank will act timidly in a few days, staying alone and hiding when possible. If the fish don't have any hiding place like caves and plants, they will swim to a corner at the bottom of the tank and stay there. So, this is expected behavior for a new fish, but if it persists, you need to find other reasons. A rise in pH levels also affects the chemical levels in the aquarium-like ammonia, which is risky.

  1. Too Much Water Current

Some fish prefer strong currents like danios, gold barbs, yoyo loach, and rainbowfish. Others prefer low currents like betta. If your fish like low currents, then strong currents can affect them, and they will tire quickly. Fish requires a lot of energy to move against the current, so they must lie at the bottom to rest.

To lower your water current, attach a sponge filter. Again, you can direct the currents towards decors and plants and break up the water force.


If your fish stay at the bottom of the tank, it can be normal behavior or a sign of trouble. Your fish may be sick or sleeping, or the tank water quality parameters are unfavorable according to the above reasons. Negative factors stress the fish making it lay at the bottom. For your fish to thrive in your tank and remain active, ensure you monitor them regularly, maintain favorable water quality parameters and observe their health.

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