The Best Fin Rot Treatments to Cure Your Fish

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Plus, symptoms, causes, and how to prevent fin rot
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Fin rot is a common bacterial disease that can affect fish—especially long-finned fish like Bettas and goldfish. While fin rot can be dangerous for fish, it can often be treated, especially if you act quickly. We’ll explain everything you need to know about treating fin rot , plus symptoms , causes , and how to prevent it from coming back , including expert tips from aquarium specialists Marshall Stephens and Craig Morton to get your fish back in good health.

How do you treat fin rot?

To treat fin rot, quarantine the infected fish to prevent the infection from spreading to other fish. Clean your tank and do frequent water changes until the pH, ammonia, and nitrate levels are correct. If moving the fish to a clean environment doesn’t slow the progression of the fin rot, treat the infection with antibiotics like API Bettafix .

Section 1 of 6:

Treating Fin Rot

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  1. Fin rot is contagious, so if your sick fish is in a tank with other fish, remove the affected fish. Put the fish in a clean tank or container with a low-flow sponge filter , a heater and thermometer , and a few decorations (like rocks or plants) so the fish has somewhere to hide. [1]
    • Most people skip substrate on the bottom of quarantine tanks—not only is it easier to set up and maintain, but it makes it easier to observe the fish.
    • Some people prefer to leave their fish in the main tank for treatment in case the other fish are infected but aren’t showing signs yet. [2]
    • Use the same type of water for your quarantine tank that you use in your main tank. For instance, if you buy water from your local fish store (LFS) for your main tank, use that in your quarantine tank as well. This will make the move less stressful for your fish.
  2. 2
    Clean your main tank thoroughly. Poor water quality is one of the most common causes of fin rot, so give the tank a good cleaning (whether you quarantined the sick fish or not). To properly clean your tank, Morton recommends that you “Scrub the glass, clean the gravel, do a water change, and clean the filter media.” [3]
    • If you have sand substrate in your tank, use a siphon to suck up any visible detritus.
    • Use a scraper to clean algae and other gunk off the sides of the tank.
    • Clean your filter thoroughly with fresh tank water, then put in new filter media. Don’t use tap water as it could contaminate the filter.
    • If you notice any rough or sharp decorations in your tank that could have injured your fish, remove them while you’re cleaning.
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  3. Siphon or scoop about half of the water from your tank, then refill it with conditioned water. [4] Consider visiting your LFS for reverse-osmosis deionized (RO/DI) water if you have a freshwater tank or commercially-prepared saltwater if you have a marine tank. This water should have consistent parameters, preventing big swings when you do water changes.
    • It’s a good idea to clean your tank before you do the water change—cleaning the tank will likely stir up sand, algae, and other debris, and a water change will help remove some of this.
    • Try to ensure the fresh water is about the same temperature as your tank water to avoid temperature swings that can be stressful for fish.
  4. 4
    Check your water parameters. Use aquarium test strips or a test kit to test your water after you change it. Your ideal parameters will depend on the fish you’re keeping, but generally, the pH should be around 7.0–8.0, the ammonia and nitrites should be 0 (or undetectable), and the nitrates should be under 30–50 ppm. [5]
    • If your parameters are still off, plan to do another 20–25% water change in 1–2 days. Keep doing these smaller water changes until your parameters are where they should be.
    • Consider taking a water sample to your LFS—they’ll be able to test more parameters and give you personalized advice on how to get your tank healthy again.
  5. If your fish’s fin rot doesn’t start improving within a few days, try adding an antibacterial fin rot treatment to its tank. Follow the dosage directions on the label—you’ll usually add a certain amount of medication based on the gallons of water in your tank, then change the water after about a week to remove the medicine. [6]
  6. 6
    Treat with aquarium salt in freshwater tanks if antibiotics aren’t available. Aquarium salt (not marine salt or table salt), also called NaCL rock salt, can sometimes help fish to overcome a bacterial infection. Dissolve the salt in a little of your tank water, add it to the tank, then remove it with regular 30% water changes once your fish starts to recover. [10]
    • For mild cases of fin rot: Add 1 tbsp (20g) of salt for every 3 US gal (11 L) of water in your tank.
    • For fin rot where the fins are starting to deteriorate: Add 1 tbsp (20g) of salt for every 2 US gal (7.6 L) of water in your tank.
    • For more advanced fin rot: Add 1 tbsp (20g) of salt for every 1 US gal (3.8 L) of water in your tank.
  7. Medications tend to leech oxygen from the tank water—adding supplemental oxygen will help keep your fish healthy. Set up an air pump or air stone in your tank to inject more oxygen into the water. [11]
    • If your fish is a Betta, set the air pump on low—a high current can be stressful for Betta fish.
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Section 2 of 6:

What is fin rot?

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  1. Fin rot is an infection that causes a fish’s fins to deteriorate. Fin rot is usually a bacterial infection and is typically caused by poor water quality, stress, or injury. Over time, the fish’s fins can deteriorate to the point that they’re completely gone, and the infection can then attack the fish’s body. Once the infection progresses to this point, it has the potential to be fatal. [12]
Section 3 of 6:

Symptoms of Fin Rot

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  1. 1
    The first sign is usually discoloration on the edge of the fin. If your fish is in the early stages of fin rot, you may see a line of discoloration along the edges of its fins or tail. This discoloration could be white, brown, red, or black. You may also notice that the fins turn cloudy, look inflamed, or have red streaks running through them. [13]
    • Depending on the color of your fish and the shape of its fins, it can be difficult to spot fin rot at this stage.
    • Some fish will also develop white or gray slime on their fins. [14]
  2. 2
    As fin rot progresses, the fish’s fins will become ragged. Stephens says, “The most common symptom of fin rot is deteriorated fins.” At this point, the infection has progressed enough that small pieces of the fin have started to fall off. This leaves the edges of the fin with a jagged appearance, and they’ll start to look shorter. [15]
    • At this point, the fin will likely regenerate as long as there’s some healthy tissue remaining.
    • If you see holes in the fins, rather than deterioration along the outside edge, the fin rot is likely caused by a fungal infection rather than a bacterial one. [16]
  3. 3
    Eventually, the fin may deteriorate entirely. If it does, you may see red streaks appearing on the fish’s back, sides, or along its tail. This means the infection is attacking the fish’s body. Unfortunately, once this happens, it can be very difficult to save the fish, which is why it’s so important to act quickly when you first notice symptoms. [17]
    • If the fish’s fins or tail are completely gone, they will not regenerate.
  4. 4
    You may notice your fish seems lethargic or stops eating. Fighting fin rot can be stressful for your fish. As the illness progresses, you may notice that your fish is spending a lot of time near the bottom of the tank, and it may not eat much. [18]
    • You may also notice your fish rubbing along the substrate, glass, or tank decorations—it’s probably doing this to relieve discomfort caused by the infection.
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Section 4 of 6:

Causes of Fin Rot

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  1. Fin rot is caused by stress. Although the infection is caused by fungus or bacteria, the root cause of fin rot is almost always environmental. The most common reason for fish to develop fin rot is poor water quality—infrequent water changes can cause your water parameters to be too high or too low, stressing the fish and making it vulnerable to disease. However, there are other factors that can lead to fin rot, like: [19]
    • Too many fish in the tank
    • Injury from sharp or rough tank decorations
    • Being bullied by tankmates
    • Contact with an infected fish
    • Cold tank water
    • Overfeeding or feeding old food
    • Handling or moving the fish

    Fin rot is often caused by gram-negative bacteria like Cytophaga , Flexibacter columnaris , and Flavobacterium columnare . [20] In some cases, it may be caused by a fungal infection.

Section 5 of 6:

Preventing Fin Rot

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  1. Stephens says, “To properly care for a tank, get into a routine and stick to it. Consistency is the key here, so you can’t skip out on maintenance.” [21] Find the schedule that works for you—some people prefer to do smaller, frequent water changes, while others prefer larger water changes spaced out more frequently.
  2. Though it may be tempting to fill your tank with lots of fish, overcrowding can lead to high stress levels and a higher risk of disease for your fish. Morton recommends that you generally should only have about “1 inch (2.5 cm) of fish per 2 gallons (7.6 L) of tank space.” [23]
    • If certain fish are nipping or biting at each other, this may be a sign that your tank is overcrowded or that those fish aren’t compatible with each other. You may need to remove the more aggressive fish from the tank—move them to another tank, try to rehome them, or see if your LFS will take them.
    • Certain fish are known to be fin nippers, including tiger barbs, serpae tetras, black widow tetras, angelfish, catfish, pufferfish, and targetfish.
  3. Stephens says to keep your fish healthy, “Choose the right size and type of food for your fish, and feed only as much as your fish can eat in about 30 seconds. Also, avoid food that just goes straight into the filter or down to the bottom.” [24]
    • Overfeeding your fish can lead to a poor immune system and put your fish at a higher risk of diseases. It can also introduce too much bacteria into the tank.
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Section 6 of 6:

FAQs

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  1. 1
    Can fish recover from fin rot? Yes, fish can recover from fin rot, especially if you act quickly once you notice the first symptoms. However, if the illness progresses to the point that the fish’s entire fins or tail or gone, it will not regrow them, and it will have a harder time recovering.
  2. 2
    Is fin rot contagious? Yes, fin rot is highly contagious to other fish. If one of your fish is showing signs of fin rot and the others aren’t, it’s a good idea to quickly isolate the infected fish in a quarantine tank.
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  • Question
    What's the best way to clean a fish tank?
    Craig Morton
    Aquarium Specialist, Aquarium Doctor Inc.
    Craig Morton is the CEO of Aquarium Doctor Inc. based in Huntington Beach California and servicing Orange County, Los Angeles County, and the Inland Empire. With over 30 years of aquarium experience, Craig specializes in creating custom aquarium designs along with aquarium installation, service, and maintenance.
    Craig Morton
    Aquarium Specialist, Aquarium Doctor Inc.
    Expert Answer
    You want to scrub the glass, clean all of the gravel, do a water change, and clean any filter media you have.
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  • Question
    How can I tell if my betta fish is sick?
    Craig Morton
    Aquarium Specialist, Aquarium Doctor Inc.
    Craig Morton is the CEO of Aquarium Doctor Inc. based in Huntington Beach California and servicing Orange County, Los Angeles County, and the Inland Empire. With over 30 years of aquarium experience, Craig specializes in creating custom aquarium designs along with aquarium installation, service, and maintenance.
    Craig Morton
    Aquarium Specialist, Aquarium Doctor Inc.
    Expert Answer
    Check your betta for cloudy eyes, white film on its skin, and torn fins. These can all be signs that something is wrong.
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    Can you treat fin rot with salt?
    wikiHow Staff Editor
    Staff Answer
    This answer was written by one of our trained team of researchers who validated it for accuracy and comprehensiveness.
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    Staff Answer
    In some cases you can treat fin rot with salt but this remedy should only be used on salt-tolerant freshwater fish. You can use tonic salt, or sodium chloride, adding 1 ounce (28g) of salt per gallon (3.7 liters) of tank water. Some fish owners advise using it only when the fin rot is particularly aggressive. You can also add aquarium salt to the water after cleaning the tank (check it’s suitable for freshwater fish), so the water is healthy––this can be done after each cleaning.
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      • API Melafix and pimafix added together to the tank works wonders, but you have to keep up with constant water changes. Make sure to remove activated carbon from the filter to get the full affect of the medicine.
      • Never use Beta fix. Always use Primafix for fin rot. A lot of people think fin rot is a bacteria but it’s really a fungus.
      • Do not overcrowd your aquarium, keep your tank clean, and don’t over feed your fish to help prevent fin rot.
      • Change 25-50% of the water daily.
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      References

      1. ↑ https://www.aquariumcoop.com/blogs/aquarium/quarantine-tank
      2. ↑ https://aboutangelfish.com/how-to-treat-fin-rot-in-angelfish
      3. ↑ Craig Morton. Aquarium Specialist, Aquarium Doctor Inc.. Expert Interview. 21 July 2020.
      4. ↑ https://aboutangelfish.com/how-to-treat-fin-rot-in-angelfish
      5. ↑ https://www.liveaquaria.com/article/89/?aid=89
      6. ↑ https://aboutangelfish.com/how-to-treat-fin-rot-in-angelfish
      7. ↑ Craig Morton. Aquarium Specialist, Aquarium Doctor Inc.. Expert Interview. 21 July 2020.
      8. ↑ Marshall Stephens. Aquarium Specialist. Expert Interview. 3 January 2023.
      9. ↑ https://blog.aquaticwarehouse.com/fin-rot-treatment/
      1. ↑ https://www.aquariumcoop.com/blogs/aquarium/aquarium-salt-for-sick-fish
      2. ↑ https://www.aquariumcoop.com/blogs/aquarium/how-to-treat-sick-aquarium-fish
      3. ↑ https://koifish.org.za/koi-fish-diseases/fin-rot/
      4. ↑ https://fishkeepingadvice.com/fin-rot/
      5. ↑ https://koifish.org.za/koi-fish-diseases/fin-rot/
      6. ↑ Marshall Stephens. Aquarium Specialist. Expert Interview. 3 January 2023.
      7. ↑ https://fishkeepingadvice.com/fin-rot/
      8. ↑ https://aquariumscience.org/index.php/10-3-4-fin-rot/
      9. ↑ https://fishkeepingadvice.com/fin-rot/
      10. ↑ https://fishkeepingadvice.com/fin-rot/
      11. ↑ https://www.sciencedirect.com/topics/veterinary-science-and-veterinary-medicine/fin-rot
      12. ↑ Marshall Stephens. Aquarium Specialist. Expert Interview. 3 January 2023.
      13. ↑ Craig Morton. Aquarium Specialist, Aquarium Doctor Inc.. Expert Interview. 21 July 2020.
      14. ↑ Craig Morton. Aquarium Specialist, Aquarium Doctor Inc.. Expert Interview. 21 July 2020.
      15. ↑ Marshall Stephens. Aquarium Specialist. Expert Interview. 3 January 2023.

      About This Article

      Article Summary X

      To treat fin rot, contain the disease by cleaning the tank and accessories in hot water and soaking everything for 5-10 minutes. Also, keep the affected fish in its own tank. If the fin rot doesn't improve in a few days, try an antibacterial fin rot treatment. You can also add 1 or 2 drops of tea tree oil and 1 ounce of tonic salt per gallon of tank water as a preventative treatment. Other preventative treatments include changing the water weekly and making sure your tank isn’t overcrowded. For more tips from our Veterinary reviewer, including how to prevent fin rot, read on!

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