Why Do Fish Lay On The Bottom Of The Fishtank?

Why do Fish Lay on the Bottom of the Fishtank?

Freshwater aquarium owners, no matter how experienced, will always get that familiar feeling of PANIC when they approach the tank and see their favorite fish laying on the bottom of the tank.

There could be any number of reasons for your finned friend to be on the aquarium floor, however, and many of them can be corrected. Let’s sink into it.

Why do Fish Lay on the Bottom of the Fishtank? Laying on the bottom can be caused by:

  • stress,
  • loud noise,
  • rapid temperature changes,
  • non-compatible fish in the fish tank,
  • fish diseases
  • overcrowded fish tank.

Laying on the bottom can be also signed of  water quality imbalances:

  • significant pH level change,
  • raised ammonia level,
  • high nitrites level,
  • high nitrates level,
  • high water hardness,
  • low oxygen level

Last but not least, Your fish is just dweller or so-called bottom feeder, and it is OK 🙂


What can cause my Fish to lay on the Bottom of the Tank?

From stress to imbalances in the water quality, fish can have periods of time where they lay on the bottom of their aquariums, seemingly not moving at all.  What causes this? For some of the most common reasons for this fishy behavior, read on.

1 – Fish Lay On The Bottom Because Of STRESS:  

Fish will sink to the bottom of the tank and possibly fade in color when they are stressed.  Stress can come from both external and internal sources.

External sources of stress can include:

  • A move from tank to tank: This is highly stressful to your fish, but can be alleviated with any number of over the counter stress relieving drops to add to your tank water.  Your fish can also be adversely affected when you move the aquarium from one place to another in your home, due to different surroundings, sounds, and lighting.
  • Loud noises: Freshwater aquarium keepers are strongly urged not to put the tanks anywhere near loud noises such as a sound system or TV.  Water acts as an amplifier for noises, and even if you have the sound turned down, the reverberations can be very distracting to your fish.  Additionally, people who tap on the glass of an aquarium can stress fish. The tapping sound is amplified; sound travels nearly four times faster in water than through the air. Some filters can be very loud to your fish, so try to invest in a filter that runs quietly to keep its vibrations from disturbing your fish.
  • Pets: If you have any pets that like to watch your fish closely, they can also be a source of stress.  Remember that your fish is very low on the food chain, so he will be on high alert to any potential predators.  If you have a cat that dips his paw into the tank, the fish can injure himself trying to escape; always cover your tanks.
  • Lighting: Your aquarium requires a proper balance of lighting and darkness.  In the wild, some fish are nocturnal, meaning they are active at night, while others are diurnal, or active during the day.  Both types of fish will require a good balance of light and dark to sleep and function as naturally as they can.

Internal sources of stress:

  • Rapid or inappropriate temperature changes:  Fish are very sensitive to temperatures and temperature changes.  It is important to be sure that your thermometer and heater are working properly, and that your heater is able to maintain the temperature required for your tank.  Temperatures that are too high can cause a decrease in the oxygen levels of your tank, while temperatures that are too low will cause the fish to be sluggish. Both extremes will lead to stress, and your fish laying on the bottom of the tank.  If temperature changes are made, make sure to make them gradually in incremental degrees to avoid shock.
  • Non-compatible fish in your fish tank:  If you have fish who are not peacefully co-existing in your tank, your fish will be stressed.  Check for ripped fins, hiding fish, or fish that seem to be aggressively chasing other fish out of his territory.  The offending finned fiend may need to be relocated to another tank.
  • Fish disease and Illness:  A sick fish will lay on the bottom of the tank, or be swimming sluggishly and in an unusual pattern.  If he has a bloated appearance, has any spots on him, has clamped fins, or appears to be having problems with his gills and breathing, you may have a sick fish who needs to be quarantined and treated.   Check for slime coat and any odd changes to the fish, such as color fading or becoming patchy. Most fish ailments can be cured with water additives and specific medications.
  • Fish tank overcrowding:  There are very stringent parameters for maintaining a quality fish tank, and overcrowding can cause imbalances that will stress the fish. Remember that your fish would be swimming in a much larger environment in the wild; you can’t put five medium sized goldfish in a five-gallon fish tank. The standard rule of figuring out the proper fish population for your aquarium is the four grams of fish per one-liter rule.   This doesn’t take into account how many decorations or plants you have in the tank, however, and remember that live plants use oxygen as well.  The shape of your aquarium plays a role as well; a ten-gallon aquarium that is taller than it is long will not allow most fish the room they need to swim back and forth but may be perfectly suited to fish who prefer to swim up and down.


2 – Your Fish is Sleeping

If your fish lays on the bottom at the same time every day or night, he could just be sleeping or napping.  Surprisingly, fish require anywhere from nine to twelve hours of sleep per night! Because they don’t have eyelids it may be hard to tell if your fish is snoozing, but there are a few other signs:

  • Slow fish movements of fin and tail:  Your sleeping fish will move his fins and tail just enough to keep himself settled in place as he sleeps.
  • Slowed fish movement of the mouth and gills:  The fish will slow down his breathing as he naps, resulting in slower movements of his mouth and gill
  • Fish is resting upright on the bottom of the tank, or under rocks and plants:  A sleeping fish will remain upright on the bottom of the tank or hide under rocks and plants while sleeping.  He may also float in place, catching his nap.

A fish can become sleep-deprived, as well, if his sleep cycle is disturbed due to the environment, light, or aggressive fish.  Your sleep-deprived fish will settle on the bottom, looking stressed and possibly losing some of his colors.

For more information on If fish can really sleep in a fish tank? dive in here.


3 – Your fish is a bottom dweller

Some types of fish are bottom dwellers or bottom feeders.  They may stay on the bottom of your tank to camouflage themselves and gather food debris or algae.  These freshwater bottom feeder fish may include:

Additionally, some eels and most snails are bottom feeders.

If your fish has a mouth that is located more to the bottom of his head, he is most likely a bottom feeder and will rest frequently on the bottom of your tank.


4 – Water Parameters are unbalanced

Fish are very sensitive to imbalances in their freshwater tanks.  From overcrowding to broken filtration equipment, a fish will become dull and sluggish, eventually laying on the bottom of his tank.  

  • Fishtank PH Levels:  

While pH levels change regularly, the most common requirements are between 5.5 and 7.5 for your fish to thrive.   A significant change in pH levels is very harmful to smaller or sick fish and may result in death. You can protect against potentially harmful changes in pH by understanding what your tank’s normal levels are and testing anywhere from twice a week, which is the recommended interval, to once per month.

PH changes in an otherwise stabilized tank can be caused by big changes in the décor, medications or other chemical additives, the addition of new fish or plants, or the need for a water change and cleaning or replacement of gravel or other substrates.  If the pH has changed after one of these events, you can observe the tank for a day or two while testing the levels to see if they return to normal. If the pH stabilizes again and your fish are not showing signs of stress or laying on the bottom of the tank, the problem has corrected itself and you can resume normal testing and monitoring of the levels.  If the fish are still showing signs of stress, you will need to address the pH levels and get them stabilized in a more aggressive way.

Increases in PH levels can also adversely affect other chemical levels in your tank, such as ammonia.

  • Fishtank Ammonia Levels:  

The standard acceptable level of ammonia in a freshwater aquarium is less than 1 ppm (part per million).  If the levels are above this parameter, your fish can suffer ammonia poisoning. Ammonia poisoning is one of the most common problems in aquariums and usually happens when setting up a new tank, when adding too many new fish to a tank, if a filter is malfunctioning, or when parasites or bacteria die off from treatment of disease. In addition to your fish laying on the bottom of the tank, you may see red streaks across its body, gills that have turned red or purple, sluggish behavior, and decreased appetite.  Death by ammonia poisoning is neither swift, not pleasant as the fish suffers from internal hemorrhaging.

If your ammonia levels are above 1 ppm, immediate intervention is required.  

  1. Reduce or stop feedings
  2. Lower the pH to below 7.0
  3. Water change of up to 50%
  4. Chemical treatment of water may be required
  • Level of NITRITES in Fishtank:  

Second, only to ammonia on the list of lethal imbalances, nitrites will rise if the ammonia level has recently risen.  Like ammonia, elevated nitrites are caused by overfeeding and the biological overload of the tank. Sometimes, a fish suffering the effects of elevated nitrites may exhibit no symptoms at all.  Other fish who have progressed to nitrate poisoning may hover close to the filtration water outlets, gasp for breath close to the surface, breathe very rapidly as witnessed by rapid gill movement, and have a tannish color to the gills. He may be listless, and as the poisoning weakens him, he may lay at the bottom of the tank in displaying extreme stress; his body may be curled upwards into a “C” position.  The poisoning occurs internally when the nitrites do not allow the fish to metabolize oxygen in his blood properly. The fish’s resistance to disease will be decreased, making him vulnerable to ich, bacterial infections, and fin rot. Because nitrites are even more deadly than ammonia in smaller amounts, the recommended level of nitrites is 0-.2mg/l.

If your nitrite levels are elevated, there are a few options to lower it safely.

  1. Up to 50% water change
  2. Add chlorine salt
  3. Consider an air stone to increase oxygen levels
  4. Reduce or stop feeding
  • Level of NITRATES in Fishtank:  

Nitrates can affect freshwater fish if the levels rise above 20 ml/l.  The rise of nitrates occurs usually in established tanks, as a result of improper cleaning, overfeeding, adding new fish, or changing the fish from one tank to another, but sudden drops in nitrates are lethal as well. If the rise has been gradual, the fish will display warning symptoms such as rapid gill movements indicating breathing distress, sluggishness, erratic and bizarre swimming patterns, and laying on the bottom of the tank. If the rise or drop is sudden, fish will die without warning in as little as twenty-four hours.  Even though the nitrate level may be high, you still must exercise caution in lowering it as a sudden drop will be just as harmful to the fish.

High nitrates can be lowered gradually by:

  1. Multiple water changes of only 5% at a time
  2. Special filtration media that removes nitrates
  3. Considering an air stone
  4. Reducing or stopping feeding
  5. Chemical intervention
  • Fishtank Water Hardness: 

Hardness in water refers to the amounts of metal ions, like magnesium and calcium.  The water hardness can affect the pH levels in the aquarium; the lower the hardness, the lower the pH.  Acceptable levels of hardness have a wide range, from 4-20 DH (degrees of hardness), depending on the species of fish.  Products are readily available to raise and lower the hardness of your water to help you achieve the right balance of pH.  Water osmosis units, water softening pillows, driftwood, peat, and bottled or rainwater are options to neutralize the hardness of your water.  For the most part, tap water is acceptable to use for most tropical fish, however.

  • Water Oxygen Level in fish tank:  

Maintaining proper oxygen levels in your fish tank is important not only for your fish but also for beneficial bacteria and plants.  The recommended level of oxygen should be above 7.0 mg/l.

How does oxygen benefit your freshwater aquarium?
  • Oxygen helps your freshwater fish:  Fish need oxygen for breathing and a healthy metabolism.  Fish who are oxygen deprived will hover near the surface because the majority of the oxygen in the tank comes from the surface.  If the fish remains oxygen deprived, he will lay on the bottom of the fish tank, eventually, die if deprived for a long enough period of time.
  • Oxygen helps beneficial bacteria in a tank:  Oxygen is needed by the beneficial bacteria in your tank to break down waste.
  • Oxygen helps your aquarium plants:  While all plants, even aquatic ones, produce oxygen through photosynthesis during the day, they will require an oxygen source at night or on overcast days.  If deprived of natural light, these plants will consume more oxygen than they release, competing with your fish. This may cause a normal drop in oxygen levels overnight.  Always provide plants with a source of daylight or a proper light set-up to encourage oxygen production.
  • Air stones are a good way to maintain oxygen levels, but the recommended way is to equip your tank with an air-driven box filter or sufficient powerhead (amazon links).  These disrupt the surface of the water, forcing oxygen down to the tank dwellers.
  • Adult fish require more oxygen than young fish, as do fast swimming fish.  Some studies revealed that after feeding, oxygen levels may lower, and the energy demand of digestion and growth can increase oxygen demand by 50%.

If you suspect your oxygen levels are lower than your fish require, the easiest step is to do a 50% water change.  This is a temporary solution, however, because if you have not corrected the problem the levels will drop again. Monitor temperatures, keep the tank clean to remove oxygen-consuming algae, and do not overcrowd the tank.

While fish need oxygen to thrive, it is possible to provide too much oxygen which can cause other issues, such as the lethal gas bubble disease.


Step by Step Troubleshooting Guide if your Fish is laying on the Bottom of the Tank

1 – Is the fish laying on his side? If he is laying on his side, he could be experiencing stress.  Remove any possible stressors and check the water parameters. If he is trying to maneuver upright unsuccessfully, he may have swim bladder disease.

2 – How long has the fish been laying on the bottom?  The fish could be asleep, or if he has been in the same position for an extended period of time (a day or more), he could be sick.  Check water parameters; if they are normal, move him to a quarantine tank and medicate him according to any other symptoms you see.

3 – Is the fish showing other symptoms? If he is gasping for air, displaying faded color, or showing blotchiness or streaks on his body, test the water immediately.  Small white spots on the fish are indicative of a parasitic process; medicate the tank.

4 – Does he come up from the bottom to eat? He may be lethargic due to an imbalance in the water or just sleeping.

5 – Is he laying still, or moving slowly?  Fish will go to the bottom of the tank to hide their eggs and sleep.

6 – Is the fish displaying the movement of the gills, fins, and tail?  If not, your fish could be deceased. Try to net him and see if he struggles or becomes alert.


What to do if Your Fish is Laying at the Bottom of the Tank

Unless other fish are displaying the same symptoms, remove the fish if he doesn’t appear to be sleeping.  Keep him in quarantine and treat for possible disease process; unfortunately, tank mates will bully an injured or sick fish.  If the other fish in the tank are all displaying the same symptoms, it will be helpful to monitor the water and medicate the entire tank if indicated.

Unfortunately, your fish may be reaching the end of his natural life cycle.  Unless you bred the fish at home, you won’t know how old he was when you purchased him.  His life cycle may be cut short if he was wild-caught or has been through significant illnesses.  Fish have a wide variety of life spans, and even with the best care, some may pass away earlier than others.

Tips for Beginner Fishkeepers

Some fish, such as bettas, spend a good deal of time laying on the bottom of their tank.  For other fish, this is an odd behavior. Ask the staff in the store where you purchase your fish what activity level you can expect in that specific species of fish.

Set up specific times for your daily care routine.  During your routine feedings, check your equipment to be sure the filter is on, the lights are working and on a good day/night cycle, and the temperature is ideal.  Use this time to monitor your fish and be sure they are all eating and acting normally.

Set up weekly routines to clean and test your aquarium.  This is an essential part of keeping your tank and cannot be overlooked.

Make sure your fish are compatible in every way. Some species require different temperatures, while some like harder water, higher pH, and longer day or night light cycles.  You can never ask too many questions when you are buying your fish, and what may make one fish happy may make another fish sick.

Start out slowly.  As exciting as an aquarium full of new fish can be, remember that the tank needs to adjust slowly to the fish to keep the water parameters healthy and do not overstock it within the first week.


Having a fish laying on the bottom of your aquarium is frightening.  While it may indicate a problem, these problems can often be fixed if they are caught early enough.  Monitoring your fish for changes in behavior, signs of illness or symptoms of imbalances in the water may be the key to keeping him off the bottom and swimming happily in his tank.

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