Fungal Infection

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What is a Fungal Infection?

A fungal infection is when a fungus grows and eats the skin, fins and body of a fish. It appears as a white, cotton-like slime on the fish. Fortunately, most fungal infections only attack the external tissues of fish.

Most infections are usually caused by a pre-existing infection or injury. Fungi are present throughout most aquariums, but certain conditions increase the possibility of fungal infections, such as poor water quality, or a stressed or injured fish.

An unclean aquarium is what usually causes the fish stress, leading to a fungal infection. Fungal infections are very contagious, so sometimes if one fish has it, it’s likely it will spread to the others. Fungal infections are commonly contracted when a fish with an infection is added to the aquarium.


  • The main sign of a betta fungal infection is white blotchy patches on the body and head of the betta.
  • Your betta may start rubbing itself against objects in the aquarium.
  • General reactions to illness will also occur, such as a loss of colour, loss of appetite, lethargy or clamped fins.

Possible Cures

It’s good practice to isolate an infected fish before treatment if your betta isn’t the only inhabitant of its aquarium. Create what’s known as a quarantine or hospital aquarium so that the treatments or medicines don’t harm your other critters or plants. If any other fish also have the infection, be sure to put them in quarantine along with the betta (or even better, create a separate quarantine aquarium for each of them). This is a good idea as fungal infections are extremely contagious.

If caught in its early phases, a fungal infection is easy to cure. It’s always a good idea to keep a look out for it. If you don’t notice it until it’s in its advanced stages, the betta won’t be as easily cured and it may not be possible to save it from dying.

What to do if your betta has a fungal infection

Once you have identified a fungal infection, the betta needs to be isolated. We recommend following these steps.  Do not follow this treatment method for more than 10 days. If this treatment does not work, try using the medication below.

1. Unless it is already at this temperature, lower the temperature of your aquarium and let it sit at anything from 75°F to 77°F.

2. Add aquarium salt to the aquarium water – 1 tsp per gallon. We recommend API Aquarium Salt – view it here on Amazon.

3. Change 80% of the aquarium water every day for the next 10 days, adding the correct amount of salt specified.

Recommended Medication

If the above advice has not worked, here is a list of fungal medications that we recommend trying. You should only try one at a time:

Medication that Uses Malachite Green

Triple Sulfa by API — view it here on Incredible Pets

Erythromycin by API — view it here on Incredible Pets

Fungus Clear by Jungle — view it here on Amazon

FIN & BODY CURE by API — view it here on Amazon

If you do try one of the above medications, we advise changing 80% of the water every day, adding the dose of medication specified by the medication’s documentation.

If one form of medication is unsuccessful, you may like to try a different one — some medication has a higher chemical level than others. Be sure to finish the course of the first medication before introducing another. Introduce the new medication, with specified doses, if the last treatment renders useless.

In extreme cases, try mixing aquarium salt with a medication course. Before starting a course, add the salt to the aquarium water; 1tsp per gallon is recommended. Be sure to pre-dissolve the salt in some aquarium water (in a clean container) before adding it to the aquarium.

Never overdose on aquarium salt

The salt needs to be at a level where it won’t harm the betta; too much salt in the aquarium water can burn the fish’s gills. The treatment of putting salt in the aquarium water should never be carried out for a prolonged length of time.  After 10 days of adding salt with the medication, discontinue adding the salt.

Once you have successfully treated your betta the fungus will disappear and you can return to caring for your betta as normal.