Fin Rot: How to Treat, Diagnose, and Prevent (2024)

Featured Image - fin rot
Featured Image – fin rot
Dr. Mollie Newton
Published by Dr. Mollie Newton PHD| Senior Editor
Last updated: July 12, 2024
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Regardless of your fish-keeping experience, whether you’re a beginner or a veteran, fin rot can pose significant challenges. This ailment can affect any fish species in aquariums, but it tends to impact those with long, flowing fins more severely. However, there’s no cause for worry. We’ve prepared an all-inclusive guide that covers the identification, prevention, and treatment of fin rot in your aquarium environment.

Article Summary

  • Fin rot is a common disease in aquarium fish that affects their fins and tails, leading to a tattered or ragged appearance.
  • To treat it, you can isolate the infected fish, check and adjust water parameters, use antibiotics or antifungal medications, and clean the aquarium.
  • The best way to prevent fin rot is through regular tank maintenance, avoiding overcrowding, separating nipping fish, and quarantining infected fish.

What is fin rot

Sick Looking Betta
Sick Betta

Fin rot is a common disease in aquarium fish that affects a fish’s fins and tail. Affected fish have a tattered or ragged appearance to the infected tail or fin. Infection can lead to loss of the entire fin, or degradation of a fish’s immune system.

Is fin rot fungal or bacterial?

Fin rot can either be a fungal or bacterial infection, it depends on the fish’s environment. When fin rot is caused by a bacterial infection the fins will appear ragged and uneven. Fin rot caused by a fungal infection is more even. Both fungal infections and bacterial infections can occur at the same time as result of a lack of treatment, poor water quality, or the fish’s immune system weakening.

What does fin rot look like

Fin rot can look different depending on the species, type, and severity of case. Generally fin rot begins as an injury to the tail or fin which then becomes infected with bacteria or fungus. As the infection progresses you’ll notice white or fuzzy lining along the edges of the tail or fins of the infected fish.

This edging is generally uneven and will leave gaps along your fish’s tail and fins. If left untreated the infection will continue to eat away the fins and tail leaving the fish with damaged or injured fins or even no fins at all. At this point, the infection will start targeting the fish’s body.

What does the beginning of fin rot look like?

When caught in the early stages you will likely only see some light fuzzy white patches on the tip of your fish’s fins and tail. At first, you might not even be sure if it’s really fin rot or may think it’s pieces of debris stuck in the fins. If you suspect one fish in your aquarium has fin rot, immediately isolate it to limit stress factors.

Fin rot signs to watch out for

Fin rot can affect not only your fish’s body but also how they act. Continue reading below to learn more about the physical and behavioral signs that may indicate your fish has fin rot.

Physical Signs of Fin Rot

As previously mentioned, you will likely notice the tail and fins start having a ragged appearance and be lined with a white fuzzy border. You might notice a red spot or raised bump from the original physical injury. Some fins and tails will experience other discoloration such as white or black.

Behavioral Signs of Fin Rot

Along with physical signs, you will likely notice your sick fish becoming lethargic and losing its appetite. You could also see some normally peaceful fish become aggressive if other fish drift too close to its injured appendage.

Fin Rot Vs Fin Nipping

Fin Nipping

Some fish species are known to be fin nippers, others might start nipping if they are in an overcrowded aquarium. While the easiest way to determine the difference between fin nipping and fin rot is observing your fish and seeing if they exhibit aggressiveness, you might not always be able to watch them.

However, fin nipping should not cause any discoloration in fins. If your fish’s fins begin to have a white fuzzy appearance or turn black around the edges it is likely fin rot.

What causes fin rot

Fin rot can be caused and worsened by a wide variety of things that change from aquarium to aquarium. Bacteria, fungus, a weakened immune system and more can all cause fin rot.

Poor Water Quality

After the initial injury poor water quality is normally what causes the infection to progress. Whether it’s caused by an overcrowded aquarium, or harmful bacteria in your aquarium water, not keeping your fish tank clean could spell disaster for your fish.

In a nutshell poor water quality can lead to more vulnerable fish because their immune system will be weakened. It’s extremely important for fish owners to commit to a regular tank maintenance schedule. Tank maintenance doesn’t just mean a water change, you should also be cleaning decor, substrate, and checking water chemistry at least weekly.


Some fish such as fancy goldfish or betta fish that are kept in incorrectly sized tanks are more susceptible to fin rot.

Aggressive Tankmates

It is important to house your fish in an appropriate environment which includes choosing the proper tank mates. Having other fish species that are not compatible can stress your fish out leading them to be more prone to disease.

A healthy fish will be swimming and exploring its environment and interacting with other fish. If you notice your fish is abnormally hiding or shying away from others it may be a sign that they are being bullied.

A bullied fish will be stressed which leads to a weakened immune system and potentially fin rot (especially if the aggressive tankmates are nippers!). Additionally, if your fish is too shy to come out from hiding it might not be getting enough fish food to stay healthy.


Aquarium fish are prone to injury. Whether it’s bumping into the glass, getting cut by sharp decor, or getting in a fight with another. An injury as simple as scraping its fin on a substrate could lead to a serious case of fin rot, especially if you don’t have a clean tank.

Poor Diet

Feeding your fish high quality food isn’t just important to keep them active and improve their coloring, it is also necessary to keep your fish healthy. Much like humans, if fish aren’t getting the proper nutrition they can be prone to all sorts of fish diseases, not just fin rot.

Can you save a fish from fin rot?

Betta with Damaged Fins
Betta with Damaged Fins

Yes, if caught early enough you can save most aquarium fish from fin rot. You should aim to treat your fish as soon as you notice discoloration at the edge of their fins. If left untreated for too long, the infection can spread to their body and become fatal. It is much easier to prevent fin rot than to treat it.

Is fin rot contagious to other fish?

Yes, any fish in the same aquarium as a fish with fin rot can potentially acquire it.

How to treat fin rot

How to treat fin rot really depends on the severity of the case and underlying features. If you just noticed the first signs of fin rot, removing your fish from the environment where it contracted the disease may allow it to heal on its own. However, more severe cases may require medication.

Quarantine Infected Fish

If you think one of your fish might have fin rot it is best to isolate it in a quarantine tank right away. This will allow you to further monitor the fish with fin rot condition as well as treat it without harming the other fish.

Be sure to size the quarantine aquarium appropriately and be extra gentle when moving the fish.

Check and Adjust Water Parameters

After removing the infected fish you should check your aquarium water with a water testing kit to see if any parameters are out of range. Not only could this explain why your first fish is feeling unwell, but it will also help you keep any other fish in your freshwater aquariums from becoming sick. Water testing kits can be purchased at most pet stores or online.

Antibiotics And Medication

Depending on what type of fin rot your fish has (bacterial disease or fungal infection) you can either treat it with a broad spectrum antibiotic or fungal medicine. These can typically be purchased online. If your fish has acquired a secondary infection it may be necessary to use multiple medications to treat and potentially cure fin rot.

Antibacterial medication usually comes in a powder form with instructions for how to dose your aquarium based on size. You will want to use a gram negative bacteria medicine as the bacteria that commonly causes fin rot, vibrio bacteria, are gram negative.

Popular anti-fungal medicines include malachite green, methylene blue, or Pimafix.


When choosing medicine make sure it is made for saltwater or freshwater fish-whichever you’re treating.

For freshwater fish many aquarists like to treat fin rot with aquarium salt (this can also be a replacement treatment if you can’t find Erythromycin).

Tank Cleaning

Cleaning your aquarium can prevent the spread of bacteria to other animals in the tank. Be sure to remove any uneaten fish food, vacuum the substrate, and clean each piece of decor. For live plants in your aquarium use a mix of 2-3mL of 3% hydrogen peroxide in 1 gallon of water. Dip your plants in the solution for roughly a minute. This will help eliminate parasites, fungus, and bacteria.

What is the best treatment for fin rot

The best treatment for fin rot is preventing it in the first place. Additionally, the earlier you catch it the better chance of curing it.

Many aquarists say Erythromycin is the best treatment, but any broad spectrum antibiotic will help. If your fish develops a secondary fungal infection be sure to change the treatment regimen. It’s not helpful to treat bacteria when the issue is a fungal infection.

What can I give my fish for fin rot?

You can give your fish a wide variety of over the counter medication that you can find at most aquarium stores. Most name brands make a fin rot treatment though some are named things like “Fin and Body Cure” or just plain “Bacterial and Fungal Treatment.” Alternatively, you can ask your vet for medication which will likely take effect much quicker.

How to prevent Fin Rot

The best way to prevent this disease is by committing to a regularly scheduled cleaning and doing research about your fish’s compatibility before placing them in the tank.

Regular Water Changes

Regular Aquarium Water Change
Regular Aquarium Water Change

Staying on top of tank cleanliness and maintenance is the best and easiest way to prevent future fin rot outbreaks. Water changes help minimize the amount of harmful bacteria in the tank, reducing the chance for infection.

Avoid Overcrowding

You should avoid adding too many fish to your aquarium. Not only will this put a strain on your tank’s bioload and filter, but it can also cause aggression among the various fish. Even those that are normally peaceful can get territorial if stressed by others or by lack of space (especially betta fish). Carefully research your specific fish species before purchasing to learn how many you can keep together and what tank size you need.

Separate Nipping Fish

If you notice any aggression, targeting, or bullying in your tank you should immediately separate the parties. Failing to do so can lead to torn fins and potentially fin rot. Betta fish are particularly prone to nipping as they are very territorial.


As soon as you suspect the fins of your fish are becoming infected immediately remove them to a quarantine tank. Be gentle during the moving process as their fins are likely sensitive and they are already stressed. Be sure that your quarantine tank is sized appropriately and continue monitoring their health.

Tank Cleaning

Committing to a regular deep cleaning schedule of your freshwater aquariums can help prevent any build up of harmful fungus or bacteria as well as give you a chance to change what you dislike about the tank.


If you’re unsatisfied with your substrate, a routine deep clean is a good time to remove it and try something else!


How long does fin rot take to go away?

The length of infection depends on the severity of the case. It can take anywhere from a few days to a couple of months to cure.

How to know if fin rot treatment is working?

If the treatment is working you’ll notice the white fuzzy edging along the fins and tail disappear, as well as your fish becoming more active and its appetite returning. The coloration of your fish should return to normal and the ragged appearance of its fins should begin to heal.

Does aquarium salt help fin rot?

Yes, while salt isn’t particularly fast at treating fin rot it definitely helps to incorporate it into your treatment regime. Aquarium salt works by gently irritating the fish’s slime coat which causes it to produce more beneficial bacteria to help fight the infection. You should add 1 Tbsp of salt per 3 gallons of aquarium water. Keep in mind that aquarium salt takes a few weeks to be effective, and you can’t place your fish in a salt bath for more than 15 minutes at a time.

Can fin rot go away with water changes?

No, while the bacteria population will diminish with every water change if your fish already has fin rot water changes will not cure it.

How often should you do water changes for fin rot?

You should change the water every time you treat your fish in the quarantine tank. While you should treat your fish in a separate tank (so that trace amounts of the medicine are not left over) I encourage you to take the time your fish is being treated and at least perform a partial water change.

If your quarantine tank isn’t established with beneficial bacteria you should perform at least a 50% water change daily to ensure the ammonia and nitrate levels don’t get out of hand.


If you’re trying to establish a new tank quickly try using biopellets.

How do you clean fin rot out of a fish tank?

If you want to completely start the tank over you can use a 2:1 solution of water to vinegar to thoroughly disinfect the tank and any decor. Be sure to thoroughly rinse the tank with clean freshwater 3-5 times after to be sure any vinegar residue is gone.

If you want to save the tank system there are two different ways to clean it.

  1. Move the remaining fish to other aquariums and allow the infected tank to cycle through for 3 weeks. Any bacteria that is left there will die as there are no hosts for it to inhabit. Just be sure to continue to dose your tank with food for the nitrifying bacteria so your system doesn’t crash.
  2.  Thoroughly clean the whole tank by performing a 75-80% water change, vacuuming all of the substrate and removing all decorations and plants to scrub them (I also like changing my filter media just in case).


While fin rot is a serious disease with hard consequences, it is easily preventable with the few tips and tricks we elaborated on above. Thanks for reading this guide, always stay informed to keep your pets happy and healthy.

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