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Fin & Tail Rot in Bettas & other Fish; Treatment and Prevention


Betta Fin Rot; Treatment and Prevention.
This applies to most ALL fish (from cichlids to arowanas), but since I get so many emails and questions pertaining to Betta Fish, this is the main subject of this article.

By Carl Strohmeyer-PAMR 35+ years experience

Updated 3/26/16

Betta Fin Rot, Ulceration
Let me first start out by noting that "Fin Rot" is a generic term that does not define any one disease, rather there are many causes of this Symptom; of which Fin Rot is better described as a symptom with more than one cause.

Often Fin Rot is brought on by injury or ammonia/nitrite poisoning, so when one considers either treating or preventing the symptom of Betta Fin Rot, these are first places to start. As well opportunistic bacteria such as Columnaris, Pseudomonas, or occasionally Aeromonas can result in fin rot (often taking advantage of fish weakened by other causes). See a picture further into this article for a picture of a Betta with Columnaris induced fin rot.

Reference: Columnaris in Fish

Finally, especially as per Bettas, genetics and age can lower a fish resistance to disease.
Unfortunately the popularity of bettas (& other fish) has led to the in-breeding of Bettas that has resulted in genetically weak fish. As well often these same less-than-scrupulous breeders will dump older Bettas on the market after their useful breeding life has passed, so a Betta you purchase may not only be genetically weak, but much older than you think! This is especially common of Bettas sold to discounters such as Walmart and chain pet stores.
The end result is a Betta that is predisposed to diseases, including fin rot, and even treatments that may work under normal circumstances will not with these fish.

Here are several points, generally in order of importance to check if your Betta or other fish has or continues to contract symptoms of fin rot:

  1. Make sure your aquarium/bowl is as close to 0 in ammonia or nitrites at ALL times; if your water starts at 0 ammonia but by the end of the week on "water change day" the level is up to 1 ppm, this is unacceptable! Do not allow your ammonia level to exceed .5 ppm
    I cannot emphasize how often I have traced back cases of Betta Fin Rot (of of more than one bacterial pathogens) to ammonia levels that are constantly in flux!

    Personally I recommend a small Sponge Filter (such as the Hydro Sponge Mini)if at all possible for a healthy bio filter.
    Recommended Product Sources:
    *High Bio Capacity Sponge Filters only from AAP
    *Hydro Sponge Mini, Betta Filter

    Prescription Bottle Bowl Matrix Bio FilterHowever I realize that many Bettas are kept in small tanks/bowls where this is not possible, but even then keeping a small amount of Matrix Bio Media (or similar high pore/capacity bio media) in a medicine/prescription bottle with holes punched/drilled in the sides to allow water through the container, while not allowing the Betta to drag his/her delicate fins across any potentially abrasive surfaces.
    Please click on this picture to enlarge.

    Product Source: SeaChem Matrix; Ammonia, Nitrates, Removing Bio Medium

    Please also read: Aquarium Nitrogen Cycle

  2. Water Chemistry parameters, other than Nitrogen Cycle (ammonia, nitrites, etc.).
    These parameters, along with a low ammonia & nitrites are important for controlling many fish diseases, not just fin rot. In fact if you are dealing with and old and/or genetically weak fish, water parameters will probably help as much as many medication treatments.

    This is an area where I think many misunderstandings/mistakes are made along with ammonia spikes.
    Often in emails, forums, and my previous aquarium maintenance "Fish Doctor" house calls, I have found that Betta keepers (& other fish too) tend to worry about pH and use products attempting to "nail down" "hard" ph numbers while ignoring KH and positive mineral ions.
    See also: Aquarium Chemistry; A to Z, Beginner to Advanced

    The KH; which are alkaline buffers plus acid buffers are more essential than a specific pH (within reason as obviously a pH of 5 or 9 is not acceptable).
    These buffers maintain a stable pH and just as importantly carbonate hardness (KH) maintains a healthy nitrogen cycle as without these carbonate buffers your nitrifying bacteria cannot thrive and you end up with even more dangerous ammonia spikes!
    Generally speaking I would recommend a KH of 50-150 ppm (for Bettas) and your pH will be just fine for Bettas as long as it is STABLE at some number between 6.5 to as high as 8.2
    Reference: Betta Habitat

    Simply put, do not chase pH in an attempt to find the perfect pH. Find an acceptable KH and stick with it, even if the pH is higher than desired as a bouncing pH can cause more disease inducing stress than the actual pH number.

    The second part of Aquarium Chemistry (GH, KH, pH) that is also important (if not more so) and also missed by many is the need for positive mineral ions (electrolytes) in the water for a healthy Betta (or other fish) immune system.
    Often Betta Keepers will use RO, Drinking, or Distilled Water without adding back these ESSENTIAL elements.
    Even when tap water is used, often products such as "pH down" or "7.0" are employed, which when used alone can drive out some essential mineral ions.
    Further Reference: Aquarium Chemistry; Positive Mineral Ions, GH

    The use of too much incorrectly treated RO water can result in Redox stress, although the flip side is attempting to make up for neglect in adding positive mineral ions too quickly which also can add stress (both are similar to rapid pH changes).
    Another chemistry stressor is oxidative stress from un-treated tap water or too high of a Redox reading (constantly over 300mV).
    Any of these before mentioned Redox can lead to a Columnaris infection that can then lead to a case of Columnaris induced fin rot (which is often a much more difficult to treat fin rot when compared to a minor cases of simply ragged fins).
    Further Reference: Importance of Aquarium Redox

    Best is a balanced approach which includes actually maintaining GH (of over 100 ppm) if only to maintain these essential mineral ions (cations) which are depleted quickly even though your GH test kit shows a higher GH.

    Using products such as driftwood fragments, Peat, Pillow Moss (AKA Frog Moss) or Atisons Spa for their Indian Almonds leaves to naturally provide a tannin acid buffer along with Alkaline Buffers such as SeaChem Alkaline Buffer is a must for use with RO water and even some tap waters.

    Recommended Product Sources:
    *Aquarium Driftwood
    *Pillow/Frog Moss; Premium Natural Acid Buffer
    *SeaChem Quick Acting Acid Buffer
    *Atisons Betta Spa

    Then the use of products such as Wonder Shells to provide a constant supply of positive mineral ions is very helpful, if not essential in small tanks/bowls to aid in constant replenishment (water changes help too).
    I recommend using 1/4 to half the recommended Wonder Shell, at least initial (by breaking in half with a flat head screwdriver), as the main goal is a constant replenishment of mineral cations, not a higher GH

    These mineral blocks come in sizes small enough for a fish bowl and can be used with Pillow Moss or even driftwood fragments to act as an acid buffer.
    Pillow Moss can be placed in aquarium filter bags (such as by Lees) to prevent it from coming apart if used directly in the aquarium.

    Recommended Product Sources:
    *Wonder Shells; Mineral Cation Replenisher; Unique Version ONLY sold at AAP
    *Lees Filter Bags

    Please read for much more; a must read!!
    Aquarium Chemistry, SE Asia Water

  3. Injury is another potential issue with Bettas and often more so with larger fish;
    With Bettas, make sure you have smooth decorations (such as marbles). Also watch for reflections that may make your Betta chase his tail (like a dog!); in fact if your Betta is dealing with symptoms of tail rot, I strongly recommend covering your tank/bowl with a towel or similar for a calming effect that can and does help.

    For larger fish, less jagged decorations also apply. With fish such as Arowanas, sometimes a bare bottom tank can prevent the fish from injuring their fins as they might dive to the bottom for food sources.
    However, sometimes with large fish, there is little you can do as the constraints of an aquarium can lead to a large fish simply injuring itself on the glass. Again, this is ESPECIALLY common with Arowanas where many cannot even turn around in the width of the aquarium often used to house them.

    The picture below shows an Arowana with fin rot most likely caused from constant contact with the glass.
    Arowana with fin rot caused from contact with glass in aquarium

    Often minor to moderate fin/tail rot from injuries caused by collisions with the tank side or objects within the aquarium are best treated either with AAP Melafix and/or Pimafix or better for more wide spectrum treatment; a Medicated Wonder Shell combined with AAP Triple Sulfa (which also improves certain water parameters too to further help with healing).
    Section 5 goes into more detail about this treatment toward the end of the section.

  4. One of the first actual treatments I would consider is a Medicated Fish bath that includes salt (Sodium Chloride), Methylene Blue, and for moderate to serious fin rot issues, a mix of antibiotics Nitrofurazon and Kanamycin.

    Recommended Product Sources:
    *Methylene Blue Aquarium Bath Treatment; from AAP
    *Furan 2 (Nitrofurazone); from AAP
    *Kanaplex (Kanamycin); from AAP

    The methylene blue is very helpful for fin rot and ulcerations caused by ammonia or nitrite poisoning.
    However Methylene Blue is not as a strong an antibacterial for gram negative bacteria, if these baths are ineffective, I would switch to Potassium Permanganate (which is a stronger oxidizer). Potassium Permanganate should be used only with salt and NO antibiotics.
    Also be careful about over dosing with Potassium Permanganate as it is a strong oxidizer where you are essentially oxidizing the "fin rot" more than the fish!
    Product Source: Jungle Potassium Permanganate, Clear Water

    Potassium Permanganate (diluted approximately 50% to 60%) or Hydrogen Peroxide can also be used as a "swab" on damaged fins or other areas of infection.

    See this Aquarium Answers post for more about how to perform such a bath or swab:
    How to Perform a Fish Bath, Medicated, Salt, more For more about Hydrogen Peroxide:
    Aquarium Medications 3, Hydrogen Peroxide

  5. Next, assuming your Betta or other fish (such as an Oscar or Arowana) actually has a bacterial infection you may have to start an in tank treatment. The most common bacterial causes of fin rot being Columnaris & to a lesser extent Aeromonas Bacterium.
    Pseudomonas bacterium may be the cause of mild fin rot infections in which the fish generally only display frayed fins and black fin edges.

    Please read these in depth reference articles and consider the suggestions and treatments there in:
    *Columnaris in Aquarium Fish
    *Aquarium Aeromonas, Septicemia, more

    The picture to the left displays a Betta with Columnaris induced Fin Rot, please click to enlarge (though not all fin rot is caused by Columnaris)

    A strong "in tank" treatment would be the before mentioned (for fish baths) Nitrofurazone and Kanamycin combination.

    Another alternative (which can also be used in baths) is Triple Sulfa.
    This is an excellent broad spectrum alternative to the Kanamycin/Nitrofurazone combination and although generally not as "strong" a treatment, it is occasionally effective when the Kanamycin/Nitrofurazone combination is ineffective.
    As well Triple Sulfa is generally less harsh on the fish and is a good choice for generally less difficult cases of fin rot with Pseudomonas as the bacterial cause.

    Maracyn Plus combines a synergistic blend of Sulfamethazine and Trimethoprim that can be effective when Triple Sulfa or Nitrofurazon/Kanamycin treatments are not effective. However, do not use this product if fish have large wounds or are suffering from septicemia, since Trimethoprim can lower blood platelets.

    Product Sources:
    AAP Triple Sulfa Broad Spectrum Antimicrobial for Fish
    Maracyn Plus from AAP with Sulfamethazine and Trimethoprim

    If this is a serious infection, most often these are caused by gram negative bacteria and treatment with primarily gram positive antibiotics such as Tetracycline or even Maracyn 2 (to a slightly lessor extent) will often be futile as the vast majority of aquarium bacterial infections are gram negative.
    Columnaris, Pseudomonas, & Aeromonas are ALL Gram negative so if someone suggests a gram positive treatment for your fish' fin rot, it is not going to be effective (unless your fish has much less common gram positive infection)!!

    Please read these articles for further reference:
    *Aquarium Medications 2; Maracyn 2, Minocycline Hydrochloride
    *Aquarium Medications Overview; Page One

    If this is a minor infection, often just the baths and/or a mild in tank treatment may help (assuming correct water parameters as addressed earlier in this article), products such as Medicated Wonder Shells or Pimafix/Melafix can help or even solve the problem.
    Melafix or better, Triple Sulfa can be an excellent first aid after a minor fin injury such as damaging a fin on a rock or even the glass in the case of large fish such as Arowanas.
    A Medicated Wonder Shell, while not a specific fin rot remedy, it still has medications that are good at addressing common secondary infections such as Saprolegnia, and just as importantly, a Medicated Wonder Shell helps with mineral Cations which in turn helps the fish in its own natural defenses in healing from a minor injury.
    When used with Triple Sulfa, a Medicated Wonder Shell becomes an excellent treatment of for fin rot caused by an injury, especially injuries that are the result of collisions with sharp objects or simply the side of the aquarium in the case of large fish.

    For Melafix use with Bettas, a pH over 7 and GH over 100 is a must!
    Melafix Myths, Dangers

    Product Sources:
    *Medicated Wonder Shells
    *AAP Triple Sulfa
    *AAP Melafix

Other Suggested Reading is:
*A Healthy Aquarium, Disease Prevention

Even suggested steps such as the use of a Level 1 UV Sterilizer should be considered if at all possible, although usually not practical for the average Betta owner.
However with larger Betta Breeders or similar multi Betta specimen tanks with dividers, the use of a UV Sterilizer may be practical.
Make sure is you are able to employ a UV Sterilizer that you change your UV bulb every six months for optimum efficiency.

Product Sources:
*True Level 1 UV Sterilizers
*Aquarium UV Bulbs, Lamps, Page 1

Other Recommended Reference & Product Sites

Aquarium UV Sterilization

The MOST in depth and accurate article about maintaining level 1 UV Sterilization and how to choose the correct UV Sterilizer

Fish Nutrition

Complete information from fish food building blocks to sources and much more

*Hikari Betta Gold Floating Pellets
Includes Astaxanthin, which helps enhance coloration, along with Grape Seed Extract has been shown to reduce the impacts of aging

Atison's Spa Clear; Indian Almond Leaf Conditioner

Clear Betta Spa contains wild almond leaf extract to simulate the natural environment of the native soft water fish.
Other natural botanicals, including Yucca extract, help control ammonia, reduce stress and maintain cleaner water.

Fusion Quiet Power, Premium Duty Aquarium Air Pumps

The Fusion has a patented baffle system for the quietest operation of any vibrator air pump

Ocean Nutrition Feeding Frenzy Feeding Station

Prevents floating food from being caught in the filter or skimmer. Excellent for Bettas kept in larger aquariums with higher surface flow rates

For a friendly, Knowledgeable, aquarium forum with in a family atmosphere:
Aquarium Forum; Everything Aquatic

*Parasite Retailers

*Planaria & Detritus Worms in Aquarium

Aquarium Decorations, Decorative Coral, Driftwood, DeCoral, PlantsDecorative Coral
Aquarium Decorations such as:
*Plastic Aquarium Plants
*Aquarium Driftwood

TMC V2 RO Filter systems; the very best you can buy with TDS meter:
Reverse Osmosis Aquarium Water Filter, TDSReverse Osmosis Aquarium Water Filters; with TDS Meter

A good compliment to RO water or for any freshwater aquarium to add ESSENTIAL Mineral Ions:
*Wonder Shells, Mineral Block

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In Chronological order of writing with the newest at the top
  1. How to Treat Sick Fish
  2. Whirling Disease in Fish
  3. Reef Aquarium Chemistry Maintenance
  4. Use of RO, DI, Softwater in Aquariums
  5. Lighting Theory of a Planted Aquarium- RQE, PFY, PAS, & PUR
  6. Aquarium or Pond Bio Load
  7. Tuberculosis in Fish
  8. PUR vs PAR in Aquarium Lighting
  9. Head Pressure in Aquarium and Pond Water Pumps
  10. Fin/Tail Rot For Betta & ALL Fish
  11. Angelfish Virus/Aids
  12. Activated Carbon
  13. Fish Baths/Dips as an aid to treatment
  14. Streptococcus gram positive bacterium in aquariums, Eye Infections
  15. Hydrogen Sulfide
    production in anaerobic De-Nitrification for Aquarium/Ponds
  16. Fish Shipping
  17. Aquarium Size, Fish Stunting
  18. Aquarium Algae,
    BBA & Brown Algae in particular
  19. Aquarium Salt (Sodium chloride) in Freshwater Aquariums
  20. Betta Habitat; Wild Bettas to Domestic Betta environment parameters
  21. HITH; Hole in the Head Disease
  22. Aquarium Protein Skimmers, Ozonizers
  23. Power Head/ Water Pump Review
  24. Molly Disease/ Mollies in an Aquarium
  25. Basic Fish Anatomy, Fin Identification
  26. Aquarium Moving/ Power Failures
  27. Octopus as Aquarium Pets
  28. Aquarium Nitrates
  29. Ichthyophonus protists, fungus in fish
  30. Aquarium and Pond Filter Media
    Types; Mechanical, Bio, Chemical
  31. Aquarium Water Conditioners (also Pond)
  32. Fish Parasites; Trematodes & Monogeneans; Annelids and Nematodes;
    Flukes, internal worms, Detritus Worms (often confused with Planaria), Micro Worms
  33. Aquarium Silicone Application;
    DIY Aquarium Repair & Glass thickness
  34. Pond Veggie Filters; DIY Bog Filter
  35. The difference between Plaster of Paris and Aquarium Products such a Wonder Shells:
    Identification, prevention & Treatment
  37. AQUARIUM TEST KITS; Use & Importance
  38. SEXING FISH; Basics
  39. Chocolate Chip, Knobby and Fromia Starfish
  40. Freshwater Velvet & Costia
  41. Usnic Acid as a Fish Remedy
  42. Aquarium Heaters; Types, information
  43. The Lateral Line in Fish, Lateral Line Disease
    or Head and Lateral Line Erosion (HLLE)
  44. Tap Water use in Aquarium; Chloramines, Chlorine
  45. Can Black Ghost Knife fish give an electric shock?
  46. Bio Wheel Review; Do Bio-Wheels really work?
  47. How do Fish Drink?
    Use of RO Water
  48. Cyclops, and Predatory Damselfly larvae
  49. Betta with Dropsy;
    Treatment and Prevention of DROPSY in all fish
  50. pH and KH problems in African Cichlid Aquarium
  51. Aquarium Gravel, which size?
  52. Blue green algae, Cyanobacteria in Ponds/Aquariums

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