Why Is My Pleco Floating Upside Down? (4 Quick Solutions)

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Fish tend to present worrying behaviors when they suffer. For example, quite a few times, I caught my plecos floating upside down at the upper sections of the tank. Luckily, as time passed, I learned what causes the issue and how to deal with it.

Plecos tend to float upside down due to a swim bladder disease, compromising the fish’s buoyancy.

That usually happens when the pleco swallows air, suffers from constipation, or carries an underlying infection. However, plecos also swim upside down when they starve and search for food at the surface.

As we proceed, I will teach you how to deal with a pleco that always floats upside down at the surface. That includes dealing with swim bladder disease and adjusting the water parameters using the API Aquarium Test Kit (link to Amazon).

Also Read: Pleco Fish Swim Bladder Disorder

Why Is My Pleco Floating Upside Down?

No one would bat an eye if they found their catfish swimming upside down. The same goes for a lionfish.[1] Such behavior is quite common in certain fish. However, you do not expect to find it in plecos, which is why any aquarist with a pleco that is swimming upside down should talk to a vet. 

The symptom normally proves that things have gone wrong with the creature’s buoyancy, in which case, you have to identify the cause, of which there are quite a few, including:

1. The Pleco Suffers From a Swim Bladder Disease

This is the most common cause of abnormal swimming behavior in fish. The swim bladder controls a fish’s movements in the water. Therefore, if the swim bladder is harmed, its functions will suffer, which can affect the fish’s motions. 

Swim bladder disease has a variety of causes, including:

  • Air Swallowing – Plecos can swallow air while feeding on the surface. Sometimes, they consume so much that it enlarges the stomach. An enlarged stomach can push against the swim bladder, compromising its functions in the process.[2]
  • Constipation – If you overfeed your plecos, or if you give them poor quality food, you can cause a blockage in their digestive tract. Constipation causes the stomach to press against the swim bladder, making it narrower and affecting its ability to control the pleco’s buoyancy.[3]
  • Inappropriate Food – If your pleco’s diet includes freeze-dried foods and dry pellets, they will enlarge in the pleco’s stomach. The stomach will expand, pressing against the swim bladder as a result.
  • Temperature – Low temperature can cause constipation in fish. This is because it slows the digestive process down, meaning that a pleco’s digestive tract can become blocked despite a proper diet constituting high-quality foods delivered in the appropriate quantities.
  • Infections – Sometimes, the swim bladder stops working as expected because a bacterial or parasitic infection has impeded its functions. You can introduce dangerous bacteria and parasites to the tank via new fish, plants, and decorations.

You can also saddle the swim bladder with infections by failing to maintain your tank. A dirty tank overrun with toxins weakens a pleco’s immune system, making the creature more vulnerable to diseases and infections.

  • Trauma – Do you have violent fish in your pleco tank? A fight between fish can cause severe injuries to the swim bladder. Plecos can also harm the organ by accidentally colliding with the walls and objects in the tank.
  • Nature – Some plecos are born with deformed swim bladders. Such plecos can live happy lives despite swimming upside down because they are accustomed to the effects of their deformed swim bladder. They won’t present as much of an issue because you would have noticed their anomalous swimming behavior from the moment they were born.

Also Read: Why Is My Pleco Floating At The Top?

2. Your Pleco is Looking for Food

Some plecos will swim upside down because they want to eat the food on the surface of the water. You may see this in plecos that don’t get enough to eat. If they are desperate enough, they will turn upside down in their search for food at the surface.

3. The Pleco is Bloated

Bloating isn’t that difficult to identify. Just look at your pleco. It won’t take you long to determine whether or not its abdomen is swollen. A bloated body can ruin a pleco’s balance, preventing it from swimming normally and causing it to sink to the bottom or turn upside down. 

Bloating has numerous causes, including:

  • Overfeeding – Like humans, you can overfeed plecos, causing their weight to balloon. Fish tend to act like they are hungry even when they are satisfied. If you respond to their actions by feeding them, the creatures will become bloated.
  • Constipation – Again, like humans, fish can become constipated. Once their digestive system backs up, they will stop passing waste. Their abdomens will also swell. The resulting expansion in their body will ruin their balance.
  • Worms – Camallanus worms can cause bloating by populating your fish to the point where you can see them sticking out of their anus.
  • Dropsy – Dropsy is the worst-case scenario. Very few fish survive this disease. Symptoms include bloating and scales that are standing up.[4]
  • Eggs – If your pleco is female, it may appear bloated because it is full of eggs. This isn’t a problem because the bloating will recede once the pleco lays its eggs.

Also Read: Why Is My Pleco Fat And Bloated?

What to do if Your Pleco Floats Upside Down?

First, make sure the pleco is still alive. You can do this by stimulating it, that is to say, touching it, adding food to the tank, performing a water change, etc. If the fish doesn’t react, then it is dead. 

But if it is still alive, you can use the following methods to remedy the factors causing it to swim upside down:

1. Treating Swim Bladder Disease

Swim bladder disease has several remedies and solutions, some of which go hand in hand, including:

  • Temperature Elevation – As you now know, a low temperature causes digestion to slow down, which is why you are encouraged to raise the temperature by a few degrees.[5] If you have a heater, it won’t take you long to achieve this objective. If you have a small tank or bowl that doesn’t have a heater, you can always use a heating pad.
  • Fasting – If the fish is constipated, stop feeding it for three days. This will give the pleco time to digest the food it already has in the stomach. The fasting will allow the stomach, which expanded because of constipation, to shrink back to its original size. For some plecos, fasting is all they need to recover from swim bladder disease.
  • Food – If your plecos are still sick despite the fasting, wait for the three days to lapse and then feed them peas. They should be cooked and peeled. Peas have a high fiber content that can make short work of constipation.

Once you resume the pleco’s regular diet, avoid overfeeding. It should only eat two or three times a day. Give the fish food that it can finish in a few minutes. Make sure the food sinks before they eat it by soaking it beforehand, especially the flaky food. If they eat from the surface, they will swallow air.

  • Infections – If you think an infection caused that swim bladder disease, you should talk to a vet. They will identify the bacteria or parasite that is to blame. They will also prescribe a solution. Either way, quarantine the fish.
  • Conditions – Maintain a clean tank with the proper pH and hardness. Use water conditioners to eliminate chlorine, ammonia, nitrites, and other toxins. Plecos with physical injuries require a conducive environment to heal.

2. Adjusting the Pleco’s Environment

Plecos in such situations require a clean, well-maintained tank. Otherwise, they won’t recover. Consider the following:

  • Water Parameters – Keep the pH between 7 and 8, the temperature between 74 degrees F and 80 degrees F, and the alkalinity between 54 and 180ppm.[6] You should install a heater if you don’t have one. This will give you more accurate control over the temperature.

To measure the pH, nitrates, nitrites, and ammonia, I personally use the API Aquarium Test Kit (link to Amazon). That bundle offers over 800 measures with high accuracy. I also use the API TAP Water Conditioner (link to Amazon) when replacing the water.

For the temperature, I prefer heaters that don’t create fluctuations. These tend to stress the fish and compromise their health. The device that works perfectly for me is the Cobalt Aquatics Neo-Therm Pro Aquarium Heater (link to Amazon).

  • Cleaning the Water – You need a strong filter that can keep the water clean. You should also perform water changes (at least 10 percent) every week. If your tank is relatively large (20 gallons and more), replace 15 to 20 percent of the water weekly.
  • Tank Size – The size of the tank will depend on the size of the pleco you have. Some plecos are small enough to survive in a 10-gallon tank. Others require 75 gallons. The size you select doesn’t matter so long as it fits the pleco in question. Avoid overstocking and overcrowding at all costs.
  • Environment – The design of the environment in the aquarium is far more critical than you realize. Stress can affect a pleco’s health, making it more susceptible to diseases that can harm the swim bladder. This is why you are expected to add plants, caves, logs, and the like to the tank. They provide hiding places. Their presence will put the pleco at ease and alleviate stress.
  • Food – You have to match the diet to the pleco’s preferences. Some plecos eat algae and little else. Others are carnivorous. You also have those that feed on wood. Try researching before adding a particular pleco to your aquarium. 

Make sure you know what it likes. A sick and stressed pleco cannot recover unless it is fed high-quality food items in the appropriate quantities. If you keep skipping meals, I highly suggest considering the Eheim Automatic Feeding Unit (link to Amazon).

  • Tankmates – You should keep plecos with fish that are as large as them. They also require friendly neighbors that are unlikely to antagonize them. Suitable candidates include Oscars, Corydoras, Gourami, and Otocinclus Catfish, to mention but a few.[7]

3. Dealing With Bloated Plecos

If your fish is bloated because of dropsy, it will most likely die.[8] Most vets agree that it is too late to save a fish whose belly is already swollen. If the pleco’s scales are not standing on end, Camallanus worms might be the cause. You can use products with fenbendazole or levamisole to fight them.[9]

If you have a bacterial infection on your hands, you can use Maracyn or any other antibiotic you have on hand. Regardless of what your fish has, it is better to quarantine a fish that doesn’t look good. That will prevent potential diseases from spreading.

4. Feeding Plecos Properly

If your pleco is floating upside down because it is hungry, but you always add food to the tank in sufficient quantities, try to remember that plecos are nocturnal.[10] They are more active at night. 

In other words, you should add food to the tank after you turn the lights off. This will ensure that the plecos are fed. If you only add food to the tank in the day, the other fish will eat it all while the pleco slumbers.

Do Plecos Float When They Die?

Yes, plecos float when they die. This is because the decomposition process produces buoyant gasses that fill the creature’s stomach.

Since gas is lighter than water, dead plecos float. Over time, the gas will run out, and the dead fish will gradually sink to the bottom of the tank.


If you found your pleco floating upside down, first check if it is alive. Stimulate the fish and see whether it reacts. If your pleco isn’t dead, the way it acts indicates an underlying issue. Start by treating swim bladder disease, which is the most common cause.

It would help if you also considered that your pleco might be searching for food. Plecos typically eat at night, which is why you shouldn’t feed them during the day. Otherwise, the other tankmates may consume everything, leaving no leftovers for your pleco.


  1. https://animals.mom.com/what-does-it-mean-when-a-fish-swims-nose-down-12626752.html
  2. https://www.aquariumnexus.com/goldfish-swimming-upside-down/
  3. https://fishkeepingguide.net/fish-floating-upside-down/
  4. https://animals.mom.com/happens-fish-gets-big-stomach-sudden-8404.html
  5. https://www.wikihow.com/Fix-Swim-Bladder-Disease-in-Goldfish
  6. https://www.aqueon.com/information/care-sheets/plecostomus
  7. https://aquamovement.com/best-pleco-tank-mates/
  8. https://www.cuteness.com/article/treat-bloated-fish
  9. https://www.aquariumcoop.com/blogs/faqs/bloated-fish
  10. https://www.fishkeepingworld.com/plecostomus/