Discus Fish Diseases, Symptoms, and Treatment

By Nadine Oraby | 2020 Update

I have already proclaimed my love of discus fish. They add so much color and vibrancy to the aquarium, but they need plenty of care because they are the sensitive kind.

Discus fish diseases, symptoms, and treatment are important topics of discussion for any aquarist. Discus fish needs proper tank conditions to stay healthy and happy. However, some diseases and infections can occur even in an ideal environment.

Your discus fish can catch some diseases while they are in the tank but it is also possible that they were already infected when you bought them. Either way, you need to be able to spot the symptoms to provide timely and effective treatment.

Common Discus Fish Ailments And Advice On How To Treat Them (Video)

Create an ideal environment for your discus fish

I have already covered ideal aquarium settings and requirements in one of my previous posts on this blog. I would recommend you to check it out, but here is an overview for those who just need a reminder.

Remember, proper aquarium conditions and water management is crucial for the wellbeing of your discus fish. You need to replicate the environment of your fish’s natural habitat i.e. the great Amazon river. Amazon water is soft, warm, and slightly acidic in general.

Just to give you an overview, these are the conditions that you need to maintain to ensure a healthy school of discus in your aquarium:

  • Temperature: 82° F – 86° F
  • pH: 6.0 – 7.0
  • Hardness: 1°-3° dKH

Other than that, you need to ensure regular change of water. Changing 50 percent of the water once a week is ideal. If the water gets too dirty, it will make your fish sick. If ideal conditions aren’t maintained, your fish will get too stressed and that is never healthy for them.

Speaking of environment, tank mates also matter to a great extent. Sometimes other fish in the tank can cause too much stress for discus. Any species that is too aggressive or messy is never a good mate for your discus.

Sometimes, other fish carry infections that don’t affect them but can prove to be fatal for sensitive fish such as discus. So, be very careful with your choice of tank mates.

Common discus fish diseases

Common discus fish diseases include bacterial infections, parasites, and discus plague. They can also suffer from poisoning due to excess of nitrates, chlorine, ammonia, or chloramine.

As a pet owner, it is your duty to give your fish a healthy environment, but there is only so much you can do. Sometimes your fish can get sick despite your best efforts and measures. So, always be prepared for the worst-case scenario no matter how careful and caring you are.

Before curing the diseases, educating yourself about them and their symptoms is extremely vital. The sooner you are able to spot the symptoms, the earlier you can start the treatment. And I don’t think I need to explain why early treatment is more effective.

Let’s talk about the symptoms that you need to keep an eye on and what those symptoms indicate.

Rapid breathing

It is normal for an overactive discus fish to experience rapid breathing. If your discus isn’t too active and you see abnormal breathing patterns, it means there can be an underlying health issue.

Rapid breathing is usually an indicator of poisoning in the tank. It can mean that the tank has an excess of nitrates, ammonia, chlorine, or chloramine.

The first thing to do in this case is to test the ammonia and nitrate levels in the tank. It is best to buy an aquarium test kit so that you can easily test the water from time to time. If the levels are fine, you can rule out poisoning, and see if there is a lack of oxygen in the tank.

In that case, you will see your discus fish swimming closer to the surface of the water and even trying to jump out. Lack of oxygen is possible if there is a highly active member in the tank.


  • You can adjust the oxygen level in the tank with the help of an air stone. Just drop one in the aquarium and you are good to go.
  • In case of poisoning, you will have to go for a specific solution such as de-chlorinator for chlorine.
  • Always make sure that the water is clean and free of decaying waste and feces of other fish.
  • Check and clean your aquarium filters from time to time to ensure optimal performance.

Leaning or laying down

Leaning on one side or laying down is not normal for a discus fish. If your fish is doing any of this or it acts as if it is losing balance, it can mean there is a serious health issue.

First of all, check nitrates and ammonia levels as they can be a cause of this problem. Secondly, see if your fish is stressed due to any reason. This mostly happens when a discus is transferred from a low-pressure environment to a high-pressure environment. For instance from a bag to a large tank, which is common during transportation.

Adding a new member in an aquarium can also cause unnecessary stress for your discus fish. They aren’t aggressive but they aren’t too social either.


  • For any problem, your first step should be to check water conditions and see if there can be any kind of poisoning. Once you have ruled that out, you can focus on other possibilities.
  • You can resolve the pressure and transportation issue by transferring the fish from a bag to a smaller tank before you introduce it to your huge aquarium.
  • If it is just stress, a spoon full of aquarium salt should be enough to solve the problem.

Fin or tail rot

It is as off putting as it sounds. You might see a fin or tail rotting and that means your water is filled with bacteria that are eating your poor pet alive. The worst part is that the rot is not reversible. What’s gone is gone but you can stop it from furthering and save your fish’s life.

Now, this is very rare but sometimes another fish can be the culprit behind a missing or nipped fin. There are many fish that do that, such as the rasboras. Once nipped, that fin can quickly catch bacteria and then the bacteria will eat the rest of it.


  • Since it is a bacterial infection, immediately remove the nipped fish from the tank. Transfer it to a smaller quarantine tank with properly tested water.
  • Test water conditions and treat the water to remove toxins from the main tank.
  • Clean your tank properly and change water.
  • Use antibacterial treatment solutions to disinfect the tank and kill all bacteria.
  • Remove all kinds of nipping fish before moving discus back in the aquarium.

Bloated or swollen belly

A swollen belly isn’t always a sign of pregnancy. It can be caused by overeating. Wait for some time to see if it goes away. If not, then it can be a sign of an intestinal blockage, or worse, a parasite. A bloated fish will also appear lazier than usual.

If it is because of food, it will go away once your fish passes it out – but you need to control and limit the quantity of food in the future. Aquarium salt is a good laxative to help your fish digest and excrete their food.

If the belly stays bloated or gets worse over time, you need to quarantine the fish and look for other symptoms. If they egest white thread-like feces, then it might be due to a parasite. If not, then it may be a blockage in its intestine.


  • Do not feed your bloated fish until you see them egest the food they’ve previously eaten.
  • Contact a vet to find the right medicine for blockage or parasite. The next section will further explain how to deal with the later.

Stringy white feces

This disease is connected to the last one. If your fish is bloated and also excreting long white feces that look like strings, then this is a clear symptom of a parasite. It can be fatal for your fish unless treated on time. In case of parasite infection, your fish is most likely to stop eating and it will become less active.


  • Immediately seek professional help to find the right medicine for the infection.
  • Move the fish to a quarantine tank and give it the prescribed medicine.
  • Check water conditions and change water regularly.
  • Add aquarium salt to ease the stress.

Hole in the head

A hole in the fish’s head is another sign of a parasite infection. Yes, it is just as disgusting as it sounds. You will see a hole in the head and that hole might get filled with puss. If it gets worse, there can be more than one hole. If not treated, this can be a fatal disease.

This kind of parasite is usually developed by poor diet combined with bad water quality. Like I said earlier, checking water quality should be your first step in any case. If you see any abnormality, resolve it before investing on any other cure or treatment.

Always ensure the water is properly clean and there is no leftover food or excess of feces in the tank.


  • For any bacteria or parasite related problem, quarantine is a must.
  • Make sure water is properly treated and tested in the quarantine tank.
  • Treat with anti-parasite medicines such as Octoxin.
  • Clean and change the water on a regular basis.
  • Use aquarium salt to help your fish with stress.

Velvet skin

Velvet skin is yet another sign of parasitic disease. It will create white velvet-like growth on the skin. Initially, it may seem like white powder or dust but it will eventually spread and turn black. Other symptoms include behavioral changes such as scratching or rubbing against other objects.

Once again, water condition and cleanliness level may be the main culprit, However, there are many instances were this parasite is introduced by another member which was added in the tank without quarantine. You should never do that. Sometimes, even plants can carry this parasite and introduce it to your tank.


  • Move the sick fish to a quarantine tank with treated water and proper conditions.
  • Treat the fish with anti-parasite medicines prescribed by an expert.
  • Calm down the stress levels with a spoonful of aquarium salt.

Skin ulcers

Skin ulcers are often caused when a wound gets infected. Let’s face it, discus fish are a bit clumsy and they often bump into rocks and other items in the tank. This can result in a wound or a cut. They can even get burned because of the internal heaters and those burns might get infected.

The infection will eventually turn the wound into an ulcer. Usually ulcers appear as a sore or an ugly red patch on the fish. If it gets worse, your fish will lose appetite and stop eating, which can be fatal.

In order to prevent ulcers, you need to be careful with what you put inside the aquarium. Make sure there are no sharp or rough objects that can cause wounds.

  • Quarantine should be your first step. Move the fish to a tank with perfect water conditions and quality.
  • Treat your fish with an antibacterial medicine.
  • Use aquarium salt to relieve stress and improve recovery.
  • Move the fish back to the community tank when the wound is healed.

Cloudy eyes

I am not exaggerating when I say you can see the happiness and health of your fish in its eyes. They are usually clear and bright. If they seem cloudy, it means your fish isn’t happy or healthy. This is usually a sign of a bacterial infection.

Now, you must be thinking why are bacterial infection or parasitic diseases so common in discus fish. They aren’t, unless water quality and conditions aren’t maintained. So, as always test the water and see what is wrong. Adjust the parameters to stop the prevalence of infections.


  • Once again, start by moving the sick fish to a quarantine tank.
  • Start the treatment with a vet-prescribed antibacterial medicine.
  • You can move your fish back once the eyes are clear again.

The discus plague

If you notice a wool like growth on your discus, it can mean only one thing; your fish has been hit by the plague. It is one of the most dangerous diseases for a discus fish! The worst part is that it is a viral infection and it can quickly spread across the aquarium.

When hit by this plague, your fish will lose its vibrancy and beauty and become all dark and slimy. It will become less active and will stay closer to the surface, as if trying to breathe oxygen from the air.

Yes, it is a deadly plague but with immediate action and proper treatment, you can save your pet. Don’t panic, be quick instead!


  • If you are sure that no other fish has caught the plague yet, quarantine the ones that have.
  • Treat them with medicines prescribed by a qualified and experienced vet.
  • Put a lot of air stones in the tank to help the affected fish breathe properly.
  • Carry out 50 percent water change every day and ensure ideal tank conditions all the time.

Related questions

Should I change the water every time my discus fish gets sick? It is indeed a good idea to change 35 percent water before you start treatment. Many diseases are caused by bad water quality. Even if you are moving the fish to a quarantine tank, it is a good idea to change the water in the main community tank to protect other fish. Leftover food and feces should be immediately removed from the aquarium.

Why is my discus fish always sick? If your discus fish falls sick too often, it means your tank conditions and water quality aren’t maintained. They are very sensitive and they require proper upkeep and maintenance. If they keep falling ill despite ideal conditions, it is best to change their food. Always go for hygienic, high-quality varieties in terms of diet.

Should I get a water testing kit? If you really care for your discus fish, then you should definitely get a water testing kit. Since discus is highly sensitive to changes in water conditions, regular testing is recommended. A testing kit will allow you to measure the level of ammonia, chlorine, nitrates, and other toxins in the tank.

Will my discus fish survive the discus plague? The discus plague may sound deadly; and it is to an extent, but it is not incurable. The secret to a successful treatment lies in early detection and diagnosis. The sooner you discover the disease, the better are your chances of treating it. With the right treatment, your fish will be ready to return to the aquarium within seven to ten days.

Will discus fish remain healthy in cold water? No, cold water will make your discus fish sick. Since they are from the Amazon, discus are used to warm and soft water. You need to maintain a temperature between 82°F to 86°F.


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