Fin Rot in Goldfish: How to treat fin rot

Fin rot isn’t a disease in itself, but rather a symptom of disease or infection.

If your goldfish has fin rot then you will notice their fins start to appear frayed or ragged, as if they’ve been torn.

You may also notice a white or red edge where the fin appears broken. Act immediately before the symptoms get worse!

In this post, we’re going to look at what fin rot is, what causes it and – most importantly – how to treat it so that your goldfish doesn’t have to suffer or even die.

What is fin rot?

Goldfish with fin rot
Fin rot on a goldfish fin

Fin rot isn’t a disease. It’s a symptom of disease or some other problem with your fish.

If your goldfish has fin rot, its fins will start to look torn and ragged, as if they’re rotting away. You might notice a red or white outline on the edge of the fin.

A fish with fin rot is likely to rub up against the side of the tank and against decorations.

What causes it?

It can be difficult to identify exactly why your fish has fin rot, as there are several possible causes. These include fighting with other fish, stress caused by injury or disease, bacteria and parasites, and poor water quality.

Poor water quality is the number one cause of fin rot.

All fish tanks contain a lot of bacteria, which isn’t usually harmful to your fish. However, when your water quality is poor, your tank can contain more “bad” bacteria and your fish can become stressed. This lowers their immune system.

A combination of low immune system and lots of bacteria can lead to bacterial infection. Meaning that bacteria eat away at your fish’s fins!

Bacterial infection is particularly likely to happen if your tank is overcrowded, your water quality is poor or your fish gets injured.

For example, if another fish nips at its fins or if it scratches itself on a sharp decoration or piece of gravel.

Unfortunately, once fin rot occurs, the injured fish and other fish in the tank can quickly make the problem get worse and worse. Affected fish often “scratch” themselves against the side of the tank or against decorations. It’s like a child with chickenpox who shouldn’t scratch, but really wants to because they’re itchy!

This can cause more damage to the fins, which allows more bacteria to infect their wounds and makes the problem worse.

Other fish often bully fish that are ill or injured. Again, this can cause more wounds, which then allows more infection to take hold.

How to treat fin rot

The earlier you spot the problem, the easier it is to treat with the right remedies.

You should therefore constantly keep an eye on your fish and look out for any sign of damaged fins.

When you spot signs of fin rot, you should quickly follow these steps:

  1. Make sure that your tank is big enough for your fish. You should have done this anyway of course, but it’s worth double-checking that your tank definitely isn’t overcrowded. It’s very difficult (or in some cases impossible) to maintain good water quality in a tank that contains too many fish.
  2. Make sure that your water quality is good. Use a test kit that measures ammonia, pH, nitrite and nitrate to check that your tank has a pH around 7-8, zero ammonia, zero nitrites and nitrates no higher than 40 ppm.
  3. Clean your tank. Hoover the gravel, clean your filter sponges (in water from your tank, not from the tap) and do a 30% water change.
  4. Use a special treatment. Buy an anti-bacterial fin rot treatment and follow the instructions on the bottle.
  5. Monitor your fish’s recovery and keep a clean tank. Are their fins starting to look better? Have they stopped rubbing up against things? Do other fish definitely not bullying them? Keep your tank clean, keep testing your water and keep doing regular water changes.

4 thoughts on “Fin Rot in Goldfish: How to treat fin rot”

  1. What if it appears that your fintail gold fish has fin rot but also is laying on its side On the bottom of the tank not swimming or anything too, moved from the tank that had a plecko that was attacking it, what all could be happening?

    • Hi Jason, thanks for your comment,
      Goldfish laying on the bottom is a key sign of stress and discomfort, this will be caused by the fin rot, it can also be caused by the treatment used to cure fin rot, especially chemical treatments witch are high in copper.
      The pleco attacking the goldfish is quite a common occurrence, what is happening is the pleco is trying to eat the slime coating off the goldfishes skin, this can cause harm to the goldfish, especially while it is under stress, I would recommend separating your pleco in a floating tub or breeder box.
      hope this helps.

  2. I have 3 comet goldfish. One of them started losing its gold color, so now its almost completely white except for some gold on its head. This does not appear like a disease, but more his color just fading away. The other 2 fish are still their normal color. Is this color change normal?


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