Fin Rot in Goldfish: How to treat fin rot

Goldfish fin rotFin 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. You should act immediately to treat fin rot 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!


What is fin rot?

Fin rot is where your goldfish’s fins start to look torn and ragged, as if they’re “rotting away”. It may look like chunks or slices of your fish’s fins are missing, your fish may rub up against the side of the tank and against decorations, and you may notice a red or white outline on the ragged edge of the fin.

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

What causes fin rot?

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, injury or disease making your fish stressed, bacteria and parasites, and – most commonly – 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, which lowers their immune system. This combination of low immune system and lots of bacteria can lead to bacterial infection, which causes fin rot, as bacteria eat away at your fish’s fins!

This 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. Fish with fin rot often “scratch” themselves against the side of the tank or against decorations (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 fin rot increasingly serious.

Also, other fish often “bully” fish that are ill or injured by nipping at their fins. Again, this can cause more wounds, which then allows more infection to take hold…

How to treat fin rot

The earlier you spot fin rot, the easier it is to treat. You should therefore constantly keep an eye on your fish and look out for any sign of damaged fins. When you do spot signs of fin rot, you should quickly follow the steps below.

  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 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? Are they rubbing against things less? Are other fish definitely not bullying them? Keep your tank clean, keep testing your water and keep doing regular water changes.

This post is part of our series on Goldfish DiseasesRead more…

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