How to Treat Fungus on Bettas

How to Treat Fungus on Bettas

Even though bettas are often sold separately from one another, they are still at risk of being sick. The typical quarantine period for fish is 4 weeks, though this will not catch certain parasites and infections. If you look at your fish one day and suddenly realize he or she has a bunch of white fluff stuck to them, you may be dealing with a fungus.

Even though most white, fluffy, and cottony looking things on fish remind us of a fungus, it is likely a bacterial infection. The external fungus can only infect dead or dying tissue, so a previous injury or bacterial infection would have to exist at the infection site. If your fish did not have an injury or previous infection at the place you are now seeing fluffy tufts, you are dealing with a bacterium.

In this article, we will discuss columnaris, determining fungus, preventing fungus, injuries, and fungal fin rot.


Columnaris is the most common form of bacteria misidentified as a fungus. Unfortunately, it is also the most deadly. This bacterial infection looks like white, fluffy patches on fish; exactly what you would expect a fungus to look like.

Unfortunately, misdiagnosing columnaris as a fungus is a death sentence for all fish involved. This disease moves extremely quickly, killing fish in as little as 24-48 hours after infection, and can wipe out a tank in a single week.

Some fish will not show any symptoms and will appear to just randomly die. This is very frustrating when trying to diagnose the issue. However, a fungus will always show symptoms (unless it is an internal infection, though these are extremely rare), while columnaris may not.

If you have a tank with rapidly dying fish and suddenly see one with fluff (commonly on the back, mouth, and body), you have columnaris.

You will need strong antibacterial medications, with a mix of Furan 2 and Kanaplex being the most effective treatment. These medications may kill the beneficial bacteria that keep your nitrogen cycle going, so you need to closely monitor your ammonia, nitrite, and nitrate levels during and after treatment.

Determining Fungus

A fungus typically can only attach to dead and dying skin. Once it latches on to that skin, it will feed on the dead flesh and move on to the healthy skin. This is common to see after injuries and bacterial infections.

The issue with this is that if you have a bacterial infection that also develops fungus, you will have to treat both. Antibacterial medications will not take care of fungus, and antifungals do not take care of bacteria.

Unfortunately, it is often dangerous to mix different medications. If the infection is external, you can do a methylene blue bath or dip in a separate container (do not use in the main tank! Everything will turn blue, and your beneficial bacteria will die).

If you do not have access to medication that can treat both at the same time, you should first treat the bacterial infection. These move faster and are more likely to kill your fish in a short time period than the fungus is.

You can also do a hydrogen peroxide swab on the affected region, which is effective against both the fungus and bacteria. Take a Q-tip, dip it in 2 or 3% hydrogen peroxide, lift your fish out of the water, gently swab the area with a Q-tip, keep your fish out of the water for another 5-10 seconds, then return it to its tank.

This will likely remove some of the fungus and will slow the growth of it, giving you time to address the bacterial infection first.

If it was a simple injury that became infested with fungus, a simple antifungal fish medication will do the trick.

Preventing Fungus

Since fungus only latches on to dead flesh, there are several things you can do to prevent the growth of it in the first place. You can reduce the likelihood of your fish injuring itself, reduce the likelihood of bacterial infections, and reduce stress.

The best way to reduce the risk of injury is to keep your water clean and test all decorations before putting them with your betta. You can test the decorations by running a tissue over any areas that may be sharp.

If the tissue tears, that means it will injure your fish. Bettas have very delicate fins, so even the slightest sharp point can tear them. If there is no dead or injured flesh to begin with, the fungus cannot set in.

Bacterial infections can arise for seemingly no reason, but it is often due to either stress or improper water parameters. You must first test your ammonia, nitrite, and nitrate in order to ensure that there is not an issue. Do not let your nitrates rise over 40ppm.

Some stressors are hard to pinpoint and may go unnoticed. There are too many to comprehensively cover here, but you can view them on our other article (name).

Stress negatively impacts the immune system of fish and leaves them open to infections, most commonly external bacterial infections. These bacteria will cause dead flesh that fungus can then attach to. Once this happens, you will have to treat both, which is tricky.


Not all injuries can be prevented, and it is very likely that your fish will get an injury at some point or another. Even with a sponge covered filter, fish can still manage to injure themselves on it.

External injuries are easy to spot and often present as missing scales or small cuts. For bettas, the most common type of injury you will see are tears in the tail.

They don’t even need to injure themselves to experience these. Since their tails are so long, they can often get “blowouts”, which are tears in the middle of the fins that do not extend to ends of their fins. This can be caused simply by the fish swimming.

Even a simple tear in the fins can lead to fungal and bacterial infections, but if the water is kept clean with a very low amount of nitrogen compounds, you can prevent infection.

Another trick for preventing infection is to add tannins to the water. Tannins make the water look like tea, which isn’t necessarily aesthetically pleasing, but they have antibacterial and antifungal properties, so they can ward off infection after an injury.

These come from tannic acid, which is leached primarily by dead plant matter, such as Indian Almond Leaves and aquarium driftwood, particularly Mopani. Adding an Indian Almond Leaf or a piece of driftwood (not cholla; bettas have a habit of getting stuck and injured on this wood) to the tank after an injury will decrease the risk of infection.

Fin Rot and Fungal Fin Rot

Fin rot is very common in bettas due to their long tails. They were not meant to have such long tails, so the circulation to the edges is often poor, and can even result in the edges of the fins rotting off. Fin rot can also be caused by poor water quality and ammonia burns.

When the edges of the fins rot and die, it is possible for fungus to set in. This can easily be cured by most fungal fish medications, and these rarely impact the biological filter, unlike antibacterial medications.

You can also do a hydrogen peroxide swab for the ends of the fins, but this is normally reserved for more severe cases and if likely not needed. Fungus eats away at flesh quickly, but less quickly than bacteria does.

In conclusion, most infections that appear to be fungal are actually bacteria. Bacterial infections tend to move much faster than fungal infections, so prompt identification and treatment is vital. The Fungus can easily be treated by a wide variety of antifungal medications and can be prevented with methods such as perfect water quality and tannins.

Leave a Comment