How to Treat Fish Diseases: 13 Steps (with Pictures)

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How to Treat Fish Diseases: 13 Steps (with Pictures)
How to Treat Fish Diseases: 13 Steps (with Pictures)

Sometimes fish are also affected by diseases. Some are easy to treat, while others are fatal. Many aquarists have a quarantine tank ready to acclimate new fish, leaving them separate from the main tank and preventing contamination by disease. If the fish becomes sick in the main aquarium, it can be removed and placed in the quarantine, which serves as a “hospital” where it will be treated.


Part 1 of 3: Identifying sick fish

Treat Fish Diseases Step 1

Step 1. Recognizing bacterial infections

Bacterial infections are accompanied by different symptoms, which can be identified through observation, including the following:

  • Inactivity.
  • Pale color.
  • Worn fins.
  • Swollen body.
  • Blurry eyes.
  • Abscesses.
  • Open wounds.
  • Red lines across the body.
  • Redness of the skin, organs or fins.
  • Difficulty breathing.
  • Protruding eyes.
Treat Fish Diseases Step 2

Step 2. Identify fungal infections

Fungal infections can be associated with other types of diseases, with the following manifestations:

  • Strange behavior when swimming, showing a tendency to "shoot" quickly from one side of the aquarium to the other.
  • Whitish material that appears around the eyes, skin or mouth of the fish.
Treat Fish Diseases Step 3

Step 3. Find out if the infection is parasitic

When the fish has a parasite infection, the symptoms will be distinct from bacterial or fungal infections. Pay attention to them, which are as follows:

  • Lack of appetite.
  • Tendency to be inactive.
  • An unusual layer of mucus in the fish's body.
  • Spots or worms apparent on the body.
  • Quick breathing.
  • Itch.
Treat Fish Diseases Step 4

Step 4. Recognize other illnesses

There are other illnesses that may not be infectious, such as tumors, constipation, wounds or even congenital abnormalities. Some illnesses can be viral. Most of them can be treated and proper filtration helps to prevent the recurrence of diseases, whether in a freshwater or saline aquarium.

Part 2 of 3: Setting up an aquarium for treatment

Treat Fish Diseases Step 5

Step 1. Find an aquarium that will exclusively serve to house a sick fish

It can be an antique that is not in use in the window or that is cheap. Do not use substrates (sand or gravel) or live plants. A filtration system that does not use carbon should be used for treatment aquariums, as carbon can “cancel” the effect of some remedies.

  • Artificial plants can be used to calm sick fish. Decorations that allow the fish to hide can also be useful.
  • The carbonless filter used should also emit little light so as not to disturb the fish too much.
Treat Fish Diseases Step 6

Step 2. Use a reliable heater

The water in the treatment tank must be kept at a good temperature for the fish, so the heater must not cause it to vary too much, keeping the sick animal very comfortable and safe. Protect it from burns by blocking any form of direct contact from the heater to the fish using a barrier such as a plastic mesh screen.

Pet shops or fish and aquarium stores may offer other options for protecting the heater

Treat Fish Diseases Step 7

Step 3. Use a porous stone

In aquariums, porous stone can be very useful to replace oxygen in the water, which is even more valid in a “hospital” aquarium, as certain remedies can interfere with the amount of oxygen in the water. Porous stones can be purchased at any aquarium supply store.

Treat Fish Diseases Step 8

Step 4. Keep the treatment tank in a dark room with a low light

Some diseases can be inhibited by little (or no) light; keeping the aquarium only in a low light and in a dark room can help fight the disease. Of course this depends on the problem, but if the disease needs light to develop, a combination of a dark place with a low light in the aquarium can be useful to treat it.

Consult an aquarium specialist at a pet store or pet store to find out if your goldfish's illness can be inhibited by reduced light

Part 3 of 3: Treating Sick Fish

Treat Fish Diseases Step 9

Step 1. Transport the fish to the “hospital” aquarium

Ensure that the water in this aquarium is as similar as possible to that of the aquarium it is used to, in terms of source, temperature and frequently applied additives, such as those that remove chlorine from the water. Prepare two other aquariums or buckets with water of at least 9.5 L, filled with water in the same way as the main fish tank. Use a net to transport him to the first bucket.

Treat Fish Diseases Step 10

Step 2. Add salt to water

Pour 3/8 of a teaspoon of salt every 3.8 L into the first bucket every two minutes, until 10 minutes is complete. Transport the fish to the next bucket of water and wait 15 minutes. After this period, do the same: fill a teaspoon with 3/8 of salt every 3.8 L added to the second bucket. Wait 15 minutes and take the fish to the treatment tank.

Treat Fish Diseases Step 11

Step 3. Treat the fish

The internet is a good source of research to determine what the animal's illness is. However, a veterinarian with experience in fish can also help with the diagnosis. Once you determine the condition that affects you, get the appropriate medication. In the treatment tank, administer the remedy following the recommended instructions.

Treat Fish Diseases Step 12

Step 4. Monitor the fish for 10 days

Keep it in the “hospital” aquarium for 10 days of treatment. Replace 30 to 50% of the aquarium water per day to keep it clean and fresh. Take the fish to a shallow aquarium every day and observe it – even with the help of a magnifying glass, if possible – to see if it is recovering and to determine if, at the end of the ten days, it will be able to return to the main aquarium..

Treat Fish Diseases Step 13

Step 5. Disinfect aquariums

To prevent the spread of the disease after treating sick fish, sanitize all aquariums using dilute hydrochloric acid or potassium permanganate. Both are available at aquarium stores and even pet stores. Follow the instructions for using the products to disinfect the aquariums; let them sit for two to three days in the container and then perform thorough cleaning and hygiene.

Fill the tank again after performing the sanitation and turn on the filtration system again so that the water returns to normal for the fish


  • Always have a simple fish first aid kit on hand.
  • Prevention is always better than treatment. Quarantine new fish.


  • Be very careful when administering fish medications and never overdose.
  • Check that the plant food used (if you have live plants) has no harmful effects on fish.

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