Fin Rot & Body Rot

This page is part of our betta disease and illness section.

We also have a handy Betta Illness Photo Guide that we send out to members of our email list. The guide includes the key points about betta illness and extra photos of symptoms.

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What is fin rot?

Fin rot is caused by bacteria eating away at your fish’s fins. Any healthy aquarium has bacteria in it — it’s what’s needed to break down waste.

Betta fish develop fin rot when kept in water that’s not clean enough. Dirty water can lead to a build up of ammonia and burn the betta’s fins. This can stress the fish out and lowers its immune system. Bacteria that thrives in dirty water can then infect the weakened betta.

Fin rot is not caused by one specific type of harmful bacteria, more so an overwhelming of aquarium bacteria. Most of the time bacteria is harmless provided that your aquarium is frequently cleaned. However, if your betta is injured for whatever reason – maybe he’s ripped his tale on an aquarium decoration, for example – this will make the fish more susceptible to fin rot/a bacterial infection.

The chances of a minor rip or wound advancing into fin rot is minor if your fish is well maintained and looked after. Only if the fish becomes stressed (which can occur due to poor keeping and/or poor aquarium conditions) its immune system will weaken thus making it more susceptible.


The damage to the fins can vary visually, but symptoms include:

  • Frayed or ragged edges
  • Fins falling apart
  • Small holes appearing in the fins
  • The edge of the fins turning red, black or white
  • The base of the fins appearing inflamed or slimy
  • The fins seeming thin, colourless or transparent

Possible Cures

It’s normal for a betta to get fin rot at some point throughout its life. Even the most experienced betta keepers have to fight this pesky problem, but it’s easily cured.

That being said, if untreated over time fin rot can  get progressively worse and sometimes develop into body rot (in extreme cases). This is what’s known as advanced fin rot, and it’s a serious threat to your betta’s well-being. Visually, the fish will have sores on it that look bloody and the fins will look much shorter than usual.

If you do need to treat your betta for fin rot, it’s good practice to isolate the infected fish before treatment if it isn’t the only inhabitant of its aquarium. Create what’s known as a quarantine or hospital aquarium so that the treatments or medicines don’t harm the other critters or plants. If any other tank mates have the infection, be sure to put them in quarantine along with the betta (or even better, create a separate quarantine aquarium for each of them).

If caught in its early phases, fin rot is easy to cure. It’s a good idea to be aware of its symptoms so that if your betta is unfortunate enough to contract it, you have a good chance of catching it early. If it’s in its advanced stages, it may be more difficult to cure your fish.

Our advice for treating mild fin rot

Method 1: Aquarium Salt

Use Aquarium Salt by API (view it here on Amazon).

1. Lower the temperature of the aquarium to about 75°F. This will delay the growth of bacteria causing the fin rot. The warmer the temperature, the more the bacteria will reproduce and grow, but you don’t want to make the aquarium too cold to the point where it’s unhealthy for the betta.

2. Add 1 tsp per gallon of aquarium salt to the water. Remember to pre-mix the salt in the water before adding it to the aquarium. It’s a good idea to place the betta in the body of water after it’s medicated with salt.

3. Do a 90% water change everyday. Treat the water with the required amount of salt each time it is changed.

4. Do not carry this treatment on for more than 10 days; it’s unhealthy to keep a betta in salt water for a prolonged period. It will damage its kidneys and give it salt poisoning.

5. If this method does not seem effective after 10 days, try method 2: mild medication.

Method 2: mild medication

Use mild Medication

Mediction that we've know to work pretty effectively is Mardel Maracyn and Maracyn 2 by Fritz Aquatics.


Maracyn 2:

How we dose Maracyn:

1. Do a 90% water change

2. Measure out half of the specified dosage of both Maracyn and Maracyn Two, then mix together and add to the aquarium.

3. Repeat this process every 3 days

If there appears to be no change after 9 days, stop the treatment. Wait 4-5 days and then try again.

If you can't acquire Maracyn, below are some other fin rot medication that we recommend. Dosage instructions will come with the medication:

Our advice for treating advanced fin rot / body rot

Use stronger dosage medication.

We've used API medications in the past — you can view it here on Amazon.

Dose API BETTAFIX with our Method 1 (aquarium salt dosage):

Simply follow our 'Method 1' dosage of Aquarium salt above and at the same time dose BETTAFIX  (instructions for the appropriate dosage for your aquarium comes with BETTAFIX).