Betta Fish Fin Rot: Symptoms, Causes, Treatment

Name: Fin Rot / Fin Melt / Tail Rot
Scientific Name: Pseudomonas fluorescens if caused by bacteria
Cause: Poor water quality or stress leading to a weakened immune system
Visual Betta Fin Rot Symptoms: Deteriorating tail and fin tips with black or red edges.
Behavioral Betta Fin Rot Symptoms: No abnormal behavioral symptoms accompany fin rot or tail rot.
Treatment: Depends on severity. Water change, Filter Change, Tropical Tank Temperatures, Antibiotics
Contagious?: Not usually contagious unless other fish have a weakened immune system.
Outlook: A full and healthy recovery is normal with fins growing back.

Betta fin rot and tail rot (melt) is a gram-negative bacterial infection or fungal infection that is extremely prevalent in betta fish. More common in uncycled tanks and small bowls, fin rot attacks and begins to eat away at a betta fish’s beautiful fins. Many bettas purchased from large box stores may already show signs of fin rot due to water quality and temperature problems in small cups.

Be careful not to confuse fin rot with fin biting, tearing, or splitting. These are due to physical injury from boredom, fighting, or snagging sharp decor. You don’t want to medicate an otherwise healthy fish. The major difference here is the lack of white, red or black edges around the deterioration.

Betta Fin Rot Causes

First things first, don’t panic because fin rot is very common and not usually deadly. It is the most common ailment amongst the species and is caused by bacteria that naturally exist in your aquarium’s water. These bacteria only become a problem when your betta has a weakened immune system which you can correct to prevent future outbreaks.

Fin rot in betta fish is normally caused by poor water conditions. Is your tank’s water temperature well under 78 degrees fahrenheit, cloudy, full of uneaten food and globs of feces? Cold water, high ammonia (>0 ppm) and nitrite levels (>0 ppm) and nitrate levels (>20 ppm) will increase stress and weaken a betta’s immune system.

Overcrowding and high bio loads from too many fish in one tank can also rapidly deteriorate water quality, increase stress, and lead to fin rot. Another cause may be inconsistent feeding resulting in overfeeding or underfeeding, causing decreased immune health.

Fin rot may also be caused by a fungal infection or another underlying disease that has caused a weakened immune system or stress. It’s possible for a betta fish to be suffering from more than one ailment at once.

Betta Fin Rot Symptoms

There are stages of fin rot varying from mild to severe which will show differing symptoms and severity. It is always best to catch any visible fin rot signs or symptoms early because it can quickly progress without attention. The Dorsal (top), Caudal (tail) and Anal (bottom) fin are the easiest fins to check and identify if fin rot is affecting your betta. For full fin descriptions visit our betta anatomy page. If left untreated, fin rot can lead to columnaris and will begin to attack the betta’s caudal peduncle and body.

  • Mild Fin Rot: Brownish fin edges, jagged fin edges, whitish tips or spots.
  • Moderate Fin Rot: Large fin deterioration and receding, black sometimes bloody fin edges, fins starting to develop fuzzy-growths.
  • Severe Fin Rot: Increased inflammation and redness of fin base, bloody fin bases, entire loss of fin or fins and fin membrane, cottony growths on the body, body rot, lethargic, difficulty swimming, susceptible to other diseases from the stress.


As a reminder, the symptoms above are very different from injuries caused by tail biting and fin nipping, fighting, or snagging tank decor. Fin tears and rips will exist without the brown or black edges and will not show the other symptoms listed above. Some breeds of betta fish are also bred to have split fins like the double tail halfmoon.

Betta Fin Rot Treatment

Treating fin rot will depend on the severity and progression of the rot. Treatment will also depend on the ecosystem and its size, and whether or not your betta is in a community tank. After classifying your symptoms above, choose the treatment and cure method that’s most appropriate for your betta.

Mild Fin Rot Treatment:

1. Check your tank’s pH level and temperature. The ideal pH is between 6.5-7.5 and the temperature should be in the range of 78-81 degrees fahrenheit. Perform a 50% water change with fresh non-chlorinated/conditioned tap water.

2. When extracting the 50% of existing tank water, use a gravel vacuum to clean the substrate of excess food, feces, and other debris. If your tank is cycled (has a filter), clean it in the tank to preserve good bacteria and replace any media that is old. Wash all tank decorations in hot water (no soap). For community tanks that are overcrowded, consider relocating some inhabitants.

3. Continue to monitor your water parameters over the next week and check for signs of healing or worsening. It can be a slow process but as you cure the rot the brownish jagged ends will disappear with new fin growth following.

Moderate Fin Rot Treatment:

1. If your betta has moderate fin rot signs or mild fin rot gets worse during treatment, you’ll need to be more aggressive. First, you should remove your betta from their main tank and place them in a quarantine or hospital tank with fresh conditioned and heated water. An ideal size quarantine tank is 1-2 gallons. Always acclimate your betta when adding them to a new tank.

2. Clean your filter in the tanks existing water to preserve good bacteria and replace any old filter media. If there are no other community members, perform a 100% water change, washing everything with hot water. This includes the tank, decor, live plants (warm water), gravel, and the heater. Replace everything and fill with conditioned water.

3. The next step is treating your betta with aquarium salt in the quarantine tank. Aquarium salt heals wounds, eases stress, and inhibits nitrite uptake. If you don’t have live plants mix fresh conditioned water with 1-2 teaspoons of aquarium salt in a separate container to fully dissolve the salt before adding it to the quarantine tank. Adding undissolved aquarium salt will cause burns to your betta fish!

4. Slowly pour in the dissolved aquarium salt and conditioned water mixture into the quarantine tank with your betta. Perform 100% water changes to the quarantine tank daily before a new dose otherwise you’re adding more salt to existing salt and overdosing which can kill your betta. Repeat this dosing for up to a week, while monitoring for signs of healing.

Severe Fin Rot Treatment:

1. Severe fin rot will require the use of medicine to reverse its damaging effects, especially if it is now combined with white fuzzy growths (columnaris). Remove your betta and acclimate them to a quarantine tank with fresh conditioned and heated water. Add an airstone or bubbler as certain medications can remove oxygen from the water. If treating in your regular tank, remove any carbon from filters as it will remove the medicine from the water.

2. Drain and clean your main tank and all of its components with hot water. Re-assemble everything, fill with fresh conditioned water, and ensure tropical water temperatures (78-81) If you have a filter start cycling the tank to reestablish the nitrogen cycle while your betta is in his or her quarantine tank.

3. Administer a recommended antibiotic in the QT following the instructions, and do not stop dosing early as this can create antibiotic resistant bacteria. Perform 100% water changes before new doses to prevent overdosing. Recommended medicines to treat severe fin rot include: Maracyn II, API Fungus Cure, API Furan-2, Kanamycin.

4. Return and acclimate your betta to their main tank after treatment and maintain clean, warm water. Make sure again that your tank is not overcrowded with tank mates.

After treatment you should see clear growths of new fin membrane starting to appear. New growths are very delicate so make sure you don’t have jagged tank decor or nippy tank mates. Fin rot can also come back after treatment and you may have to do additional treatments to keep it away for good.

Make sure you’re taking care to prevent the causes of fin rot that are listed above. Also, new fins don’t always grow back looking the same, sometimes they are slightly shorter, longer, or even curled at the edges.

Preventing Betta Fish Fin Rot

The best way to avoid the anxiety and treatment of fin rot is to avoid it altogether. Keep your tanks water clean, heated and not overcrowded. Fin rot is more common in smaller, uncycled ecosystems like bowls which are not adequate environments for a betta. The correct size is 5 gallons with 2 being the absolute minimum.

The smaller the tank, the quicker bacteria builds up and water quality declines. A five gallon tank should have water changes once a week with smaller tanks requiring changes every 3-4 days or more. If your betta fish currently is experiencing fin rot, we wish him or her a speedy recovery.


4 Responses

  1. Tammy

    My betta is eating and swimming great but he looks like he is ” fin nipping” but when I do my research I think that it’s fin rot! When I show everyone his picture they all say he looks fine! I don’t get it why his fins look like he took a bite of of his fin

  2. Johann

    Great article about fin rot. I like that you have decided between different strength of treatment.

    Regards, Johann

  3. Christina Marie Parissi

    I can’t tell if my fish is fin nipping or has fin rot either and I am very confused. Should I take him back to Petco and ask? He’s a very active fish and he eats well. He is in a half gallon tank. I know that is very small but I live in an apartment and can’t have a big tank. He has lived almost a year. We believe my previous Betta died of an infected swim bladder. I am very scared for Sebastian, my current fish. I have anxiety and watching him is very comforting. I was/am very attached to my fish because I can’t have children and can’t afford to take care of a dog or cat. Sebastian did injure himself about 6 months ago on some decor, the sore healed but I don’t know about his tail, whether it ripped or not. He is a red delta. I would appreciate some more input on what to do. Thank you.


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