Fin Rot – How To Prevent (And Treat)

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Fin rot is a common disease of bettas and other freshwater aquarium fish. This condition causes discolored, damaged, or jagged fins, and can even end in death. Fortunately, you can beat fin rot and return your fish to perfect health with the right knowledge and treatment plan.

This article teaches you everything you need to know about this condition, as well as how to treat it, and how to prevent it from coming back. We’ll focus mostly on betta fish fin rot, but the same information applies to pretty much all other freshwater fish.

Let’s get started!

What You Need To Know (The Facts)

NameFin rot, tail rot, betta fin rot, fin melt
Common TreatmentsAquarium salt, antibiotic medications, antifungal medications
CauseBacterial infections (e.g. Pseudomonas fluorescent) or fungal infections caused by stress from poor water quality, low water temperatures, injury, etc.
Common SymptomsDiscolored, rotting fins and tails that can become frayed, develop holes, or rot away completely.

What Is Fin Rot?

Fin rot is a common condition of betta fish and other fresh and saltwater species that can be deadly if left untreated. It is usually a secondary condition, which means it develops as a result of another problem like stress or injury.

This disease is very common in betta fish, but it can affect many different species, especially fish with long fins. Fin rot can be caused by a bacterial infection, a fungal infection, or both.

Diagnosing fin rot can be tricky in the early stages, but as it progresses, the symptoms become quite noticeable. Here’s what to look out for in affected fish:

Betta with Fin Rot


  • Mild fin rot – Color changes on the betta’s fins can be seen. The fin tips and outer edges of the infected fins and tail often turn whitish as the infection takes hold.
  • Moderate fin rot – The edges of the damaged fins and tail begin to rot away. Major fin damage begins, creating ragged, uneven edges and slightly ripped fins.
  • Severe fin rot – The fish fins can become badly torn and even develop holes. As the fin rot symptoms progress, your fish will begin to lose their appetite and become inactive.
  • Advanced fin rot – Fins can be lost completely as the disease progresses.
  • Extreme fin rot – The infection can spread to the fish’s body in very severe fin rot cases, causing body rot. Fin regrowth may not be possible once this stage is reached.

Which Fish Are Affected?

Any aquarium fish can be affected by fin rot infections, but some species are more vulnerable than others. The following fish are especially susceptible to fin rot:

Preventing It In Freshwater Fish

The good news about fin rot is that it is very preventable. This disease does not usually affect healthy fish out of the blue so you can definitely prevent it by maintaining a healthy aquarium.

We’ll get into some more details later in the article but let’s start by listing the most important things you can do to keep your fish healthy:

  • Cycle your aquarium before adding fish
  • Make sure you have (and use) a filter, heater, water conditioner, and aquarium test kit
  • Keep your tank clean
  • Use only aquarium-safe substrate and decorations
  • Feed your fish a healthy diet
  • Research the needs of your fish
  • Choose the right tank mates and avoid overstocking

Treating mild fin rot is often very successful, but prevention is always the best option. Let’s take a closer look at the key steps for preventing fin rot in betta fish and other species.

  1. Choose Healthy Fish

Fin rot often starts before you bring a betta fish home. This is especially true for betta fish that are kept in cups without heating and filtration. These fish really need a larger tank of at least 2.5 gallons (preferably 5 gallons +) to stay healthy. If you can’t purchase a fish from a good fish store, consider purchasing from an online store.

  1. Keep The Water Warm

Temperature is very important for maintaining a healthy immune system. Many new fish owners make the mistake of keeping betta fish in unheated aquariums, and this can really suppress their immune systems.

Make sure you have an aquarium heater set to the right temperature and use a thermometer to verify its performance.

  1. Provide The Right Water Parameters

Stress is a major cause of fin rot in betta fish and other fish species. Some fish have quite specific needs and will be easily stressed in the wrong water parameters. Use your water test kit to measure your pH and hardness before buying your first fish.

  1. Maintain High Water Quality

The harmful bacteria that cause fin rot might occur naturally in your aquarium, but that doesn’t mean all your fish will get sick. Stress and poor health allow the infection to take hold. Fin rot often happens when fish are under stress and kept in poor conditions.

Poor water quality is usually the result of a lack of maintenance, overstocked tanks, and uneaten fish food that is left to spoil.

You’ll need good filtration to keep the water in your tank clean and prevent fin rot. Regular maintenance is equally important, however, so use your aquarium water test kit regularly and perform a partial water change every one to two weeks.

Your water parameters should read:

  • Ammonia: Zero parts per million
  • Nitrites: Zero parts per million
  • Nitrates: Less than 40 parts per million (ideally less than 20 ppm)
  1. Choose The Right Tank Mates

Fin nipping and fighting can also cause stress and injury that often results in fin rot. Choosing compatible tank mates is really important, so always research a fish carefully before adding it to your community tank.

The following fish are notorious fin nippers:

  • Tiger barbs
  • Dwarf puffers – like pea puffers
  • Silvertip tetras

The type of tank mates you keep is important, but you should also be careful not to keep too many fish in your aquarium. Overcrowding can cause fighting and poor water quality. If you are overstocked, you might need to split your fish up into two aquariums or move them all into a bigger tank.

  1. Avoid Sharp Decorations

Fin rot can sometimes be a simple trauma that looks like an infection, but it is mostly caused by bacteria, fungus, or a combination of both.

Fish with long, flowing fins are very susceptible to injuries caused by sharp objects. Fish tank decorations and artificial plants often have sharp edges, so be sure to inspect them carefully and file down any sharp points or edges before adding them to your tank. Manufacturers like Marina make great silk plant products that won’t harm your fish’s fins.

Great For Delicate Fins!
Marina Naturals Plants

Silk plants that are designed to be gentle on fish with fancy fins like Bettas and Fancy Goldfish

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  1. Avoid Overfeeding

Overfeeding fish can cause direct health issues like obesity, or negatively affect your water quality as uneaten fish spoils on the substrate. Feed your fish only as much fish food as they can finish in a minute or so and be sure to remove any leftovers.

How To Treat On Fish (How To Cure)

Prevention may be the best way to deal with fin rot, but what do you do if your fish is already infected? Fin rot is a condition that gets worse and worse so it’s important to treat it as soon as possible. Fortunately, treating fin rot is quite easy in its early stages.

Read on to learn how to cure fin rot on your fish.

Before Treatment

Before starting with chemical treatments, I always recommend removing the cause of stress. Remember, fin rot is usually a secondary infection, which means something has weakened the fish and made it vulnerable.

Here’s a quick checklist to help you find any possible causes:

  1. Are your fish fighting? Observe your fish to see if there’s any fin-nipping or bullying going on. The offending fish might need to be moved to a separate tank.
  2. Are your water parameters correct for your fish? Use your test kit to check your nitrate, nitrite, ammonia, and pH levels.
  3. Is your water flow too strong? A strong water current will make weak swimmers like betta fish tired and stressed.
  4. Is your water temperature correct? Use a thermometer to check that the aquarium water is warm enough for your fish.
  5. Do any of your ornaments have sharp edges? Run your fingers over your decorations. If they feel sharp, you’ll need to sand them down or remove them from the tank.

Hopefully, after going through these questions you will have found your cause and be able to take the necessary steps to correct the problem.

Start With A Water Change

A large water change (up to 80%) and thorough tank cleanup are the first steps in treating fin rot, so go ahead and prepare some fresh water and add some water conditioner to make it safe. Bring this water up to the same temperature as your tank to avoid stressing the fish.

Use your gravel vacuum to suck up as much waste as you can from the substrate while removing old water. This is the perfect time to clean off the surfaces of the glass, hardscape, and decorations in your tank. After changing the water, you should have brought your nitrate levels right down and have a clean and healthy aquarium.

You can treat your fish in your main tank if you have just a single betta fish or if more than one of your fish is affected. Using a quarantine tank to treat your fish can be the most effective way of treating fin rot, however.

You can easily treat your sick fish without the disturbance of the other tank mates this way, and you don’t risk harming aquatic plants and inverts like snails if you treat your betta fish with aquarium salt.

Read on to learn how to set up an inexpensive quarantine tank to treat fin rot.

Setting Up A Hospital Tank

A separate small fish tank or separate container is a very important tool for treating sick fish and quarantining new fish before adding them to your community tank. You can put together a hospital tank very cheaply.

Here’s what you’ll need:

You can use a normal tank or any fish-safe container that holds between 5 and 20 gallons, depending on the size of the fish you keep. You won’t need any lighting or substrate, but a small sponge filter, a heater, and a hood will be necessary. An ornament or a soft plastic plant will complete the setup.

Which Medication To Use

There are many medications that can be used to treat fin rot. Let’s take a quick look at some of the recommended products and what they are used for:

General Medications

Cure-all medications like API General Cure are very useful treatments for curing fin rot. It does not target fin rot directly but rather cures the fish of primary infections that may be weakening their immune system and causing an infection on the fish’s fins.

This medication can be used in combination with other general treatments like aquarium salt or more targeted treatments like antibiotics.


The actual infection that causes fin rot symptoms is either bacterial or fungal in nature. You can target bacterial fin rot directly by using an antibiotic like Mardel Marycn.

The active antibiotic in this medication is known as erythromycin, but you can also use antibiotics that contain tetracycline/doxycycline or furan. These medications should be used in a hospital tank.

Antifungal treatments

An antifungal medication like Ich-X can be very effective for treating fungal fin rot. This is a great product to keep on hand because it works really well for treating other common fish diseases like ich.

How To Use Aquarium Medications

It is generally best to follow the dosage and usage instructions supplied by the manufacturer. They have tested their products extensively and calculated the ideal dosages for you. Some aquarists have had great success by changing doses and combining medications, however.

Some experienced fishkeepers, for example, recommend a combination of API general cure and a 0.3% aquarium salt dose. Another popular method is to combine doses of antibiotics and antifungal treatments to target whatever type of fin rot the fish may have.

Remember to remove any activated carbon/charcoal filtration media before dosing. This medium absorbs chemical medications before they can get to work on the bad bacteria and fungi that make your fish sick.

Treatment With Aquarium Salts

It is possible to treat fin rot without medications by using aquarium salt. The downside to this fin rot treatment is that aquarium salt can harm live plants. This can be avoided by treating your betta fish (or other fish) in a quarantine tank.

Aquarium salt is not quite the same as regular table salt, so make sure you get your salt from a fish-keeping store, rather than the kitchen. Add one-half to one teaspoon of aquarium salt per gallon of water in your aquarium.

It is best to dissolve the salt in aquarium water before adding it to your tank. Continue this treatment for a few days while performing daily water changes. You’ll need to add more salt each time you change the water to maintain the right concentration, but be careful not to add too much as this can kill your fish.

Frequently Asked Questions

Can fish survive this?

Fish can survive fin rot and make a full recovery. If the condition progresses onto the fish’s body, however, it may be too late. Treating fin rot before it becomes severe is the best course of action.

Can this heal itself?

Fin rot can heal itself if the cause of stress is removed and the fish’s immune system is able to recover. Fish will often make a full recovery after simply making a water change, cleaning their tank, reducing stress, or increasing the aquarium water temperature. Treating your fish is a safer option, however.

What is the main cause?

The main cause of fin rot is stress. Poor water quality, physical injuries from fighting or sharp decorations, and cold water temperatures are common causes of stress that can trigger fin rot symptoms.

How long does it take to heal?

Fin rot can improve in just days with the right treatment. Recovery time will depend on how severe the damage is, however. Fin regrowth can take several weeks in advanced cases.

Can betta fish recover?

Betta fish fin rot is something that they can definitely overcome. Start by addressing the cause of the stress, and use the appropriate medications to treat this common condition before it becomes too advanced.

Is it contagious?

Fin rot is contagious in the sense that the same stressors can result in multiple fish developing the condition at the same time. The bacteria and fungus that cause the symptoms are usually present all the time, but they can multiply in aquariums with poor water quality.


  • Enany, M. E., et al. “Bacterial causes of fin rot in some fresh water fishes.” Proc. 6th Int. Symp. on tilapia in Aquaculture. Manila, Philippines, Sept. 20041.
  • Khan, Hamid. “Study in diseases of fish: Fin-rot—A bacterial disease of fins of fish.” Proceedings/Indian Academy of Sciences. Vol. 10. No. 6. Springer India, 1939.
  • Pungkachonboon, Temdoung, K. Tajima, and Ong ard Lawhavinit. “GC analysis of Mycobacterium sp. isolated from siamese fighting fish (Betta splendens Regan).” Seminar on Fisheries 1991. Bangkok (Thailand). 16-18 Sep 1991.. 1991.

Final Thoughts

Betta fin rot and body rot can be very serious conditions for betta fish and other fish in freshwater aquariums. Fortunately, this is one fish disease that can be treated successfully at home. Remember to tackle this problem by figuring out the source, rather than just treating the infection, that way you can get rid of fin rot and make sure it doesn’t come back!

Have you treated betta fish fin rot in your aquarium? Let us know how you won the fight in the comments below!

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