treating fin rot

What Exactly Is Fin Rot? Causes, Symptoms & Treatment

Fin rot is particularly common among tropical fish, especially those who are kept in freshwater aquariums. Fortunately, this health condition is easy to spot because its physical manifestations are very specific. The fins of aquarium fish typically have smooth or consistent edges.

Fish with fin rot have jagged and gradually receding fins. It usually occurs on the tail but it can affect the dorsal, pectoral, anal and pelvic fins as well. It can also coexist with other health conditions such as dropsy.

If not treated as soon as possible, the fish may die due to bacterial infection and have impaired mobility and balance.

How Can I Cure Fin Rot?

Let’s get straight down to the reason why you are here. You’re looking for a way to treat fin rot because your fish is showing symptoms. I’ve never been one to beat around the bush, so let’s start with the cure…

Although fin rot is prevalent, it is highly treatable. Medication such as Melafix and Aquarisol are usually added in the aquarium water to kill the bacteria that causes fin rot.

The best method to treat Fin Rot is to kill the harmful bacteria in your aquarium with a product like Melafix.

We have used Melafix for years with no adverse effects and with a very high success rate for treating the disease. It’s the gold standard of fish medication and should be sufficiently stocked in the cabinet of every aquarium owner.

symptoms of fin rot

Not All Medication is Safe to Use

Drugs such as Tetracycline, Oxytetracycline, malachite green methylene blue and Chloramphenicol are also used to treat fin rot. However, take note that medication can be stressful to fish. They filter the water through their gills so they are ingesting significant amount of the medicine.

There are some instances that fin rot is accompanied by fungal infection. Fin rot usually starts from the edges of the fins and tails. However, if you see holes then it’s a likely indication of fungal infection.

If the fin rot is rapidly spreading, meaning the fins and tails recede significantly within 24 hours, then it could be a columnaris infection.

What Causes Fin Rot?

There are many identified causes of fin rot. Fin rot itself can be a disease or a symptom of a more serious health problem but the root cause of this disease starts from the environment. It could be caused by other fish in the aquarium.

Because fin rot is a disease caused by gram-negative bacteria such as Vibrio, Pseudomonas and Aeromonas, it can be transmitted to other fish through physical contact and infected aquarium water. In other cases, a fish nips the tail and fins of other healthy fish. This can become infected and result to fin rot.

Overcrowded Tank
Overcrowded Aquarium

An overcrowded aquarium risks the fish to fin rot. Water quality becomes poor, pH fluctuates, and levels of nitrite and ammonia increases due to waste products.

Aquarium water that is too cold can also contribute to fin rot.

Feeding your fish with outdated food or leaving large amounts of food floating the entire day can build a breeding ground for bacteria that causes fin rot.

Stress also contributes to fin rot. Playing with your fish, handling and moving them to another aquarium improperly can stress your fish. Some fish are territorial and dominant so their presence can stress other fish in the tank. If you introduce a new fish, it helps to rearrange the decoration to “reset” their surroundings.

What Does Fin Rot Look Like

Signs of fin rot

The most notable physical sign of fin rot is the presence of uneven white, fuzzy lining on the edges of fins and tails. The fins and tail may turn more opaque or milky. They may appear inflamed or blood streaked.

Soon, they would start to fray and appear ragged. In most cases, fin rot is only noticed when it’s in its advanced stage, that is, when pieces of the tail and fins start to fall off and the white edges become thicker. White dots can be present sometimes.

Fin Rot Behavioral Signs

Your tropical fish can feel that their fins and tail are slowly disintegrating. Fin rot causes the fish to become listless. Your fish may also attempt to seek relief by rubbing itself against the tank and aquarium decorations. If fin rot is caused or aggravated by nipping, the fish will feel stressed or “bullied.” Overall, fin rot doesn’t cause any other behavioural problems.

Best Fin Rot Treatment

treated fish

Fin rot in fish is typically caused by bacterial infections, though fungal infections can also be a secondary problem. To effectively treat fin rot, follow these steps:

  • Water Quality: Ensure your aquarium has optimal water conditions. This includes checking parameters such as ammonia, nitrite, nitrate, pH, and temperature. Poor water quality is the leading cause of most aquarium diseases. A water change of 25%-50% can help reduce the spread and provide a better environment for healing.
  • Aquarium Salt: Adding a conservative amount of aquarium salt can assist in healing, as it helps to prevent secondary infections and stimulates the production of the fish’s protective slime coat.
  • Antibacterial Medications: Over-the-counter treatments specifically designed for fin rot can be effective. Common options include API Melafix and API Fin & Body Cure. Always follow the manufacturer’s instructions and ensure the chosen medication is safe for all inhabitants of the tank.
  • Isolation: If you have multiple fish and only one is affected, consider moving the sick fish to a quarantine or hospital tank. This prevents the spread of the disease and allows for easier treatment.
  • Consult a Veterinarian: If the condition doesn’t improve or gets worse, consult an aquatic veterinarian.

How To Prevent Fin Rot From Reoccurring

preventing fin rot

Separate Nipping Fish

When buying your tropical fish, make sure to check the fins and tails carefully. Be aware how mild and severe fin rot looks like so you can take a close look at each fish species of your choice.

As mentioned, fin rot is a bacterial disease so if you introduce an infected fish to the aquarium, the bacteria can spread to other fish as well.

As soon as you notice fin nipping activities, separate the fish. Nipped fins can become infected.

Regularly Change Aquarium Water

Since the fish’s environment is the main contributing factor to fin rot, make sure that you change the aquarium water periodically. Be sure to use a water conditioner anytime you add new water to the tank. These are very important to reduce chemicals in the water that could be harmful to your fish.

The frequency depends on the size of the aquarium and the number of fish in it but generally, 1 gallon of uncycled water should be replaced every 3 days whereas a 5-gallon tank every 7 days.

Take note that uncycled doesn’t mean unfiltered. High concentrations of nitrite, nitrates, and ammonia are conducive to abnormal bacterial growth.

Clean aquarium water is the best prevention. You may also add a pinch of aquarium salt to your freshwater tank to act as a mild antiseptic. We love this one from API.

Please keep in mind, however, that aquarium salt should not be used if you have a scaleless catfish.

Quarantine Infected Fish and Clean Tank

If you notice one of your fish developing fin rot, isolate it immediately so it won’t affect other fish. Clean the aquarium and rinse the sand and all decors with boiling water to disinfect them. Use a screen filter when rinsing the sand so food debris and other waste are washed away.

Keep An Eye On What You Have in The Tank

You can also add live plants such as Java moss and Java ferns. Keep the temperature of the aquarium and the pH at proper and stable levels.

Fish food that is left in the aquarium gets stale, thwarts the water’s pH and eventually becomes a breeding ground for bacteria so it helps to feed your fish small amounts periodically rather than sprinkling a large amount once and thinking it would last the entire day.

Buy fish food in amounts that can be consumed within 2 months to ensure that it hasn’t lost its nutritional value.

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  1. Thank you so much, this was very helpful and my fishes are now better than ever

  2. Anonymous says:

    Very very thankyou, it saved Steven one of my Japanese kois. I am too happy!

  3. Mark donaire says:

    Thanks for the ideas..

  4. Hi
    I’ve got 5 goldfish in my tank but one looks really unwell. I even thought it had lost an eye at one point.
    Put fin rot treatment in water and it started to clear up but it’s just as bad now and all around it’s mouth
    Any suggestions?

  5. “Clean the aquarium and rinse the sand and all decors with boiling water to disinfect them. Use a screen filter when rinsing the sand so food debris and other waste are washed away.”

    Forgive me since I’m a newb to keeping fish, but wouldn’t that really put a hit on the beneficial bacteria in the tank? I got knocked off my cycle a few weeks ago and just recovered a couple days ago where both ammonia and nitrite are at zero and nitrate is at around 20ppm. I just noticed a male guppy’s back fin looks a little damaged and his body seems sort of like he had a rough night out. It’s sort of hard to describe. But he’s not looking his best. Is this just coming down to boiling things will save my tank of fish VS dealing with a new cycle to contend with?

    I also have notice that on a different species of guppies, they have white dots on their rear fins, but no where else on their bodies. No other fish have white dots, just that one particular type of guppy.

    1. Hi Alyssa! That’s a great question.
      Infected fish and aquarium water can cause fin rot to spread to healthy fish, so your best bet will be to disinfect with boiling water. Think of it like weighing the scales. You might save beneficial bacteria, but you’ll also expose your fish to harmful bacteria.

      Guppies with white dots can signify the Ichyophirius parasite or simply guppy ich. I’d recommend monitoring them for signs of the condition. Also, how is your male guppy?

    2. Leslie Sullivan says:

      My sons betta fish had fin rot in January and I treated it. The fins started growing back but now I can tell it’s back again. What do I do? The previous treatment must not have cured it all the way.

      1. Hi Leslie. Recurring fin rot is pretty common but nonetheless concerning. What’s the duration of recurrence? It’ll help you rule out biting, as you treat the fins. Also, I’d recommend getting a sponge filter if you don’t already have one, since they harbor good bacteria.

  6. Shannon B says:

    I got a betta it’s like my 10th or 12th I had him alone in a 30 or 40 gallon tank anything like he was just kind of getting bored so I got two Corey little bitty catfish and a female betta means SpongeBob and date the betas for playing and the catfish were doing what they do and yesterday morning I looked and crimson my bettas bins were mostly gone with like the little I guess bone sticking out and they’re just mostly gone so would fin rot happen overnight and could it be a fin rot from biting and would it be more likely that it was the little catfish nipping on him because one of them is kind of aggressive

  7. Shannon B says:

    I got a betta last summer a baby.It’s like my 10th or 12th I had him alone in a 30 or 40 gallon he started to seem bored this new year. So I got two Corey little bitty catfish and a female betta we named SpongeBob and. The betas are very nice with each other playing while catfish were doing what they do and yesterday morning I looked and crimson my bettas find were mostly gone. I guess bone sticking out and they’re just mostly gone so would fin rot happen overnight and could it be a fin rot from biting and would it be more likely that it was the little catfish nipping on him because one of them is kind of aggressive?

    1. Shannon B says:

      He did not have any fin damage only day and they were mostly gone the next.

    2. Hi Shannon. I’m sorry to hear about your bettas. Given the details, your betta fish likely sustained those injuries from aggression-related activity. Fin rot is rapid, but it often won’t occur so drastically overnight. I hope this helps!

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