Tackling Fin Rot In Your Pond Fish

If you have chosen to have a pond in your outside space, you are likely to have also chosen to stock it with ornamental fish, koi or the many other types of fish. Whilst you can easily look after their environment and physical needs, their health needs may need a little more focus. For example, fin rot can be a very debilitating health condition that fish contract.

What Does Fin Rot Look Like?

You may not notice fin rot to begin with as it can start as a very small red patch, usually at the base or edge of the fins. However, if left untreated it can rapidly grow until it destroys the fins and it can even spread to other parts of the mouth and body. The fins will look frayed and there may be patches of skin that look bloodstained.

What Are The Effects Of Fin Rot In Fish?

Even if you do not see the rot straight away, your fish may exhibit symptoms. These can vary, but usually they will take the form of lethargy and loss of appetite, which may be difficult to spot if you don’t see the telltale signs on the fins.

What Causes Fin Rot?

There can be a few causes of fin rot, but usually they are all environmental. For example, poor oxygenated water can allow bacteria to build up. Additionally, overcrowding can also help diseases to breed. If your fish is not the healthiest when you buy it, then it may deteriorate when placed in conditions like this. Once the bacterial breeds it attacks the membranes of the fin. This then leaves the fish vulnerable to fungal infection. Koi and goldfish are very sensitive to fin rot.

Can It Be Cured?

Yes, fin rot can be easily cured. Not only that, it can also be prevented from taking hold.


Once you have identified the fish(es) with fin rot you should isolate them from the rest of the fish. You will need to buy an anti-bacterial treatment and add this to a separate tank of water. Ensure the tank has plenty of aeration, either by oxygenating plants or a pump. The anti-bacterial treatment can also be used to prevent fin rot in the first instance.

How Long Before My Fish Are Better?

Once you have given treatment your fish will seem brighter quite quickly, however, it will take a few weeks or so before the fins start to re-grow. Your fish may still have scarring after the regeneration, but that is nothing to worry about.

Preventing Further Outbreaks Of Fin Rot

Once you have treated the fin rot you should treat the bacterial in your pond. The water will need to be tested for nitrates as well as the pH level. Remove any decaying vegetation and clean the filter. You will also need to exchange about half of the water with rainwater if possible. If you don’t already have an aeration system in place it is worthwhile considering installing one as this will help any future outbreaks.