Why Fish Stay at the Bottom of the Tank & How You Can Help

If you’re feeling panicked because you’ve noticed that your fish are laying on the bottom of your tank, then know you aren’t alone. Whether you’re an experienced fish owner or you’re a newbie, seeing your favorite swimming friends sitting at the bottom of your aquarium can be distressing.

Why do fish stay at the bottom of a tank? If you notice that your fish are hanging out at the bottom of your aquarium, there could be several reasons for this. Your fish could be experiencing stress, temperature changes, have non-compatible fish in their tank, fish diseases, an overcrowded area, water quality imbalances, or because your fish happens to be a bottom feeder.

Since there isn’t a lot of information on the Internet today about why fish sometimes crowd at the bottom of the tank, we’ve created this article to help you out. Below we’ll cover some of the reasons why your fish might be spending too much time on the lower end of your aquarium and what you can do about the issue. 

Causes of Bottom Dwelling

If you’re wondering why your fish seem to be spending a lot of time hanging out at the bottom of your fish tank, then know that there are several reasons for this issue. If your fish is laying at the bottom of your fish tank, then consider the items we’ve listed below, which may be one of the reasons why your fish are staying at the lower end of your tank.

  • Your fish could be stressed out. 
  • Your fish might be in a room where they hear too much noise. 
  • Your fish could be feeling an unwanted temperature change. 
  • You don’t have compatible fish in your tank
  • Your fish could be experiencing fish diseases.
  • You have too many fish in your fish tank. 

Another reason why your fish might be spending too much time at the bottom of your tank could be water quality imbalances. Water quality imbalances include the following:

Another reason why your fish might be lying at the bottom of your tank is that your fish is a bottom-feeder. So, if that’s the case, then nothing is probably wrong. However, if you know that your fish is not a bottom-feeder, then any one of the above issues is perhaps causing your fish to crowd at the bottom of their tank. 

Fish Stress 

Your fish might be hanging out at the bottom of your aquarium because they are stressed. When fish are stressed, their color starts to fade, and they naturally sink. There could be many reasons why your fish is stressed out, including external sources of stress and internal sources of stress. We’ll cover both in a little more detail below. 

External Fish Stress

There can be many reasons why your fish is experiencing external stress, which we’ve listed below.

Tank Move

Your fish could be stressed because of a recent move from one tank to another. When fish are moved from tank to tank, the entire experience is very stressful. If you want to avoid stressing your fish out, purchase some over the counter drops for fish stress at your local pet store. Also, if you’ve moved your tank from room to room recently, the change of surroundings could be the cause of your fish stress.

Noise Pollution

Noise pollution can also create a high-stress environment for fish. You want to avoid placing your tank in a place that has a lot of noise, like a television or a sound system. Water amplifies sound, making noise even louder for your fish inside the tank.

You should also make sure none of your friends or family members are tapping on the glass of the tank. Tapping on the tank’s glass can scare your fish.

Also, check on your tank’s filter. Some tank filters are noisier than others for your fish. You’ll want to make sure you get a quiet filter so that your filter doesn’t wind up stressing out your fish.


If you have other pets around your fish like dogs and cats, they probably like to stare intently at your fish for hours. Other pets can stress your fish out easily. That’s because fish know they are prey to both dogs and cats. Since your fish might get hurt when trying to escape a swipe from a random paw, you want to keep your tank closed at all times and covered.

Also, if your other pets are doing far too much fish watching and stressing your fish out, put your tank in a room where the other pets can’t access the container. That way, your fish can relax and get back to normal again.


Your fish also need a balance of light and darkness. Some fish are nocturnal and active only at night. Other fish are diurnal, or proactive when it’s daytime. No matter what type of fish you have, you’ll need a balance of dark and light so that the fish can function similarly as they would in the wild.

Internal Fish Stress

If you feel your fish could not possibly be experiencing any external sources of stress, then you might have an internal fish stress issue. Internal fish stress can come from several factors, which we cover below.

Fast Temperature Fluctuations

Your fish are susceptible to climate fluctuations, including temperature. That’s why you need to make sure the thermometer and heater in your tank are both correctly functioning if you suspect an issue with your fish. Ensure that your heater can keep the temperature level your fish needs while inside your tank.

If your fish are stuck in a tank that has a temperature that’s too high, you’ll wind up with less oxygen in your tank. Less oxygen can make your fish act strangely, including staying at the bottom of the tank because they don’t have the oxygen they need to be active. A temperature that is too low will make fish slow as well because they won’t be warm enough to move around comfortably.

Whether your tank is too hot or too cold, your fish will feel stressed and start pooling around at the bottom of your aquarium. So, you’ll need to change the temperature, but you’ll have to make sure you very slowly change the temperature inside the tank, so the fish don’t go into shock.

Your Fish Aren’t Compatible

If you haven’t spent enough time doing your research and you are new to keeping your fish in an aquarium, you might have put fish in your tank that isn’t compatible. If you have fish that don’t get along together nearby, all of your fish will experience stress.

Before you add a different type of fish into your tank, always make sure it’s compatible with the fish you already have. You can still do a quick Google search or ask somebody at your local pet store. If you suspect you may have fish that aren’t compatible in your tank together, you’ll need to look for fish injuries, fish that are hiding, or fish that are chasing around other fish often.

Fish Disease

Another reason why your fish might be spending too much time at the bottom of your aquarium could be a fish disease. If fish seem sluggish or are swimming unusually, those are signs of fish disease. Other things to look out for include a bloated appearance, unusual spots on your fish, frozen fins, or noticeable breathing issues with gills.

If you notice any of those potential issues with any of your fish, then you’ll need to quarantine and treat your sick fish. You’ll need to remove sick fish from the general population because the fish disease can quickly spread to the other fish. Also, do a complete water change for the healthy fish in your tank.

When you remove sick fish from your tank, look for slime on the fish’s coat or any other changes like color fading or a patchy appearance. Most types of fish disease can be handled with some medicinal water additives.

Overcrowded Fish Tank

Another reason why your fish could be experiencing internal sources of stress is fish tank overcrowding. If you have too many fish in your tank, that alone can cause the water to feel imbalanced. If the water isn’t balanced, your fish will become naturally stressed out. Keep in mind that in the wild, fish are used to having unlimited space.

So, remember that you should have about four grams of fish for every one-liter you have in your tank. Keep in mind that your decorations don’t factor into that equation but should be considered appropriately. Also, if you have real plants in your tank, they’ll help create more oxygen.

You Have Sleepy Fish

Many new fish owners don’t realize that fish sleep, but they do. Fish need to sleep about nine to twelve hours each night. However, since fish don’t have eyelids, figuring out if they are napping can be difficult. If you suspect your fish might be sleeping, look for:

  • Slight movements on the fin and tail.
  • Slow use of the fish’s mouth and gills.
  • Resting fish will be upright on the bottom or hiding under rocks or plants.

Just like people, fish can become sleep deprived. If your fish is experiencing stress because of light, noise, or other fish in the tank it doesn’t get along with, your fish will become sleep-deprived.

Your Fish is a Bottom Dweller

If your fish is a natural bottom dweller or bottom feeder, then they’ll prefer to hang out around the bottom of your aquarium. That’s because they blend into the environment more naturally, and they can eat the debris and algae they crave. Freshwater bottom-feeding fish can be:

  • Corydoras catfish
  • Kuhli Loach
  • Otocinclus
  • Snails
  • Plecostomus
  • Eels
  • Freshwater sharks
  • Algae eaters

If you’re not sure how to tell if your fish is a bottom feeder, look for a mouth that’s located toward the bottom of its head. If you see a mouth there, then you probably have a bottom-feeding fish that feels more comfortable at the bottom of your tank.

Unbalanced Water Parameters 

Water imbalances can also severely stress out fish, making them sluggish and slow. When the water in your tank is imbalanced, your fish will prefer to rest on the bottom of the tank because their environment won’t let them do much else. That’s when you’ll need to start checking on the water levels in your tank.

PH Levels

It’s widespread for pH levels to fluctuate often in your tank. However, the healthiest pH levels for your fish are from 5.5 to 7.5, which will allow your fish to prosper. If the pH level fluctuates drastically, smaller or sickly fish will probably wind up becoming fatalities. You can avoid these types of harmful changes in pH by knowing what the normal levels should be. You should also test your levels at least twice a week with pH testing strips.

Ammonia Levels

Another thing you’ll need to check on is the ammonia levels in your tank. The level of ammonia you’ll want in a freshwater tank is lower than 1 ppm (part per million). If the ammonia levels in your tank are higher than this, then your fish could get poisoned by the ammonia in the water.

Ammonia poisoning is an often overlooked issue in many personal fish tanks. You can wind up with high ammonia levels if you have too many new fish in your tank, your filter isn’t working right, and when parasites or bacteria are killed because you’ve treated a fish disease.

Having too much ammonia in your tank can leave your fish acting sluggish, and they’ll start hanging out at the bottom of the tank. Also, you might see red stripes, red or purple gills, lazy behavior, and less appetite. Fish can feel very sick from ammonia poisoning, so if you have it, you’ll want to act quickly. Start by testing your tank with some ammonia strips.

If you test your tank and you realize your ammonia levels are too high, you’ll need to do the following:

  • Cut back feeding or stop feeding altogether.
  • Get the pH levels in the tank below 7.0.
  • Perform a 50% tank water change.
  • You may need to treat your water, too chemically.

You’ll also need to check on the nitrate levels in your tank. If the ammonia in your tank is already high, your nitrites are probably even high. A rise in ammonia usually also causes the nitrate levels in your tank to rise as well. When your nitrite levels are too high in your tank, your fish won’t act the way they usually would.

If your fish are experiencing nitrite poisoning, they will stay close to filtration water outlets, breathe rapidly, gasp for air, and have gills that look tannish. Fish that are suffering from nitrite poisoning also won’t act the same. You’ll notice a decrease in activity as your fish hang out at the bottom of the tank because of the stress the fish feels.

When fish experience nitrite poisoning, they won’t be able to metabolize oxygen in the blood correctly. That means your fish will have a decreased immune system, and they can’t battle against illness. Your fish then become vulnerable to a wide range of bacterial infections. So, you’ll want to make sure you check the nitrate levels in your fish tank with some strips. Make sure your nitrates are at the level of 0-.2mg/l. If your nitrite level is above that, then you’ll need to take steps to lower it. Here’s what you can do:

  • Perform a 50% water change. You can do multiple water changes of about 5% at a time to gradually do this and not shock your fish.
  • Cut back or temporarily stop feeding
  • Put some chlorine salt in your fish tank
  • Add an air stone to your tank to boost the amount of oxygen in the tank.
  • Ass a unique filtration system that will get the nitrites out of the tank.

Final Thoughts

If you’ve noticed that your fish are spending a lot of time at the bottom of your aquarium recently, then you do have some cause for concern. Your fish could be spending time at the bottom of your fish tank for any number of reasons. Your fish could be feeling stress, a temperature shift, have non-compatible fish in their tank, fish diseases, an overcrowded area, water quality imbalances, or because your fish happens to be a bottom feeder.

If you aren’t sure exactly what the problem is, you need to check the levels in your tank using the steps we provided above and make sure there are no chemical imbalances inside the aquarium. If so, you’ll need to take action and get your fish’s environment back to healthy levels.

However, if you’ve checked the levels in your tank and you still aren’t sure what’s going on with your fish, you’ll need to check for signs of disease. If you suspect infection, you can purchase several products to help your fish recover so that they are healthy and happy again