Why Is My Koi Fish Losing Scales?

If you notice that your koi fish has been losing its scales, it is probably an indication that something is wrong with it.

This could not just be harmful to the koi but also to the rest of the tank mates.

Fortunately, there are several ways to care for your koi fish losing scales. Continue reading this guide to learn more about koi fish losing scales and how to treat them.

Why Has My Koi Fish Suddenly Started Losing Scales?

This happens to koi fish typically due to either some stress or because they are sick.

You can see ulcers or sores on their skin when their slime coating (which protects them from illnesses) is damaged.

In order to get some relief, koi might be seeing flashing. This means they will try to rub their bodies off a rock or some other surface to get the itching to stop.

This could also be one of the reasons why their scales fall off.

It would be better if your aquarium does not have any sharp objects to prevent koi from rubbing themselves against it. This could result in an open wound or death in extreme cases.

How to Identify Koi Fish Losing Scales?

If your koi fish is losing scales, it is pretty easy to find out when this is happening. The loss of scales is clearly visible on a koi fish.

Moreover, you may also observe that your koi fish’s color has become darker, and wounds and skin rash will become more visible. Apart from this, you will also find their scales floating on the surface of the water.

Besides this, the fish might isolate itself from the others. Watch out for signs like loss of appetite, damaged fins, or skin rash.

The disease is more likely to spread and worsen if the infected koi fish is not isolated from the rest of the tank mates.

If you feel any of the fish is sick, you should immediately isolate it from that pond. A net could be helpful in safely removing the particular koi.

The best way to prevent a koi from losing its scales is to ensure that the environment that they are in is suitable.

This will surely lower their stress levels and make sure they are more potent at fighting off diseases.

Do Scales Grow Back for Koi Fish?

The good news is that koi fish scales start growing back after recovery. Like most fish, koi are also consistently regenerating their scales, so you can expect to see a new layer once that happens.

In short, even if your koi has lost some scales, it is not a cause for concern as the cells will reproduce and eventually grow new scales once they are healthy.

On average, koi fish starts regenerating cells after one to two weeks post-recovery. The recovery process is dependent on how regular the mealtime is.

The more frequent and the healthier your koi fish’s feed is, the faster the recovery process. Therefore, you should focus on restoring your koi fish to health as soon as possible.

In some cases, you may notice that the scales are not growing back on your koi even after several weeks.

When this happens, it means that there is something wrong with your koi. This mainly occurs when your koi is severely sick or under a parasite attack.

Besides this, you may also check the tank water and ensure it is at the right temperature. If the temperature is off, your koi may take longer to recover.

Alternatively, keep checking your koi’s diet and add more protein to it to speed up recovery.

If all the above measures fail, take your koi fish to the vet to figure out why the scales are not growing back.

Why is My Koi Fish Stressing Out and How to Prevent It?

A change in environment can make koi fish vulnerable. One of the most valuable methods to prevent this is to ensure a safe and healthy environment inside the tank.

Even though koi fish will undergo a bit of stress whenever they are put in a new environment, you should always ensure the following conditions remain the same.

The Quality of Tank Water

If the condition of the water is not adequate, it can harm the koi fish’s health. Besides pH level, there are other variables to consider, such as temperature, ammonia levels, and salinity.

An ideal pH level for koi fish would range from 6.8 to 8.2, and the oxygen levels are recommended to range from 5 mg/L to 18 mg/L. Besides this, the temperature of the water is to be maintained from 65° – 75° F.

The salinity levels are preferred to be on the lower side, 1kg salt/1000liters for regular use, and you can increase it by a small margin if you want to treat a koi disease.

This can be checked regularly with the help of a digital salt meter.

In a higher quantity, ammonia proves to be dangerous for the health of fish. Since they excrete ammonia, a proper filtration system should be set up to ensure no buildup. An ideal pond would have ammonia levels close to 0.

In order to find out the nitrate & nitrite levels, test kits can be used. Ideally, a range of 20 – 60 parts/million is the optimum range for a koi pond. Koi fish can only be at risk if the level of nitrate exceeds 300 ppm.

The quality of the pond’s aeration, as well as filtration, is closely related to the quality of the water. To prevent ammonia buildup, filter media or mechanical filters can be used.

If the pond has still water, then it depicts that the filtration is poor. Oxygenated water is essential when it comes to breaking down ammonia and other pollutants in the water. The bacteria need oxygen to do so.  

In addition, a fountain waterfall design is also another option for keeping the pond water aerated. Not only does a fountain look aesthetically pleasing, but it will also help aerate the water more regularly.

Alternatively, you can also add more aquatic plants or an air pump to the pond to regulate the oxygen levels in the water.

Diseases or Parasite Attack

Even though koi are strong fish, they can still suffer and lose scales due to illness or a parasite attack.

However, this can be taken care of by ensuring the water quality is above par since most of the infections are transmitted through the water itself.

Moreover, they can also catch an illness from some other source, like perhaps if you add a new fish to the sick pond.

You should always ensure that each fish is healthy and not sick before you add it to the pond.

You should constantly monitor the pond to check for fin rot, slime coat deterioration, and other signs. Another thing you need to look out for is dropsy, which can lead to bloating in fish.

Another big issue that leads to illnesses is overcrowding. Always ensure that the size of the pond is fit for the number of koi that are present in it.


If there is a predator such as a heron or any other small mammals, this will increase the stress levels of koi. The koi fish pond should be made in such a way that predators cannot access it.

It also ensures that the pond has enough depth that a heron cannot stand, ensuring it cannot harm the fish inside it.

If the pond is near trees and has a shade over it, this will also protect it from the aerial view of a heron. An electric fence or a pond net could also come in handy.

Another problem that should be considered is the nitrite content in a koi pond.

You can install features such as aquatic plants to provide shelter or hiding spots for your koi fish. Water lilies, hornworts, or other sheltering structures can also prove to be helpful.

It is also essential to monitor the behavior and condition of your koi carefully because it may not always be easy to tell if your pond has predators or not.

If your koi fish have damaged fins or torn scales, then it could mean that a predator is present in the same pond. You can also install a camera so you can monitor your pond even if you are not present near it.

Poor Quality of Food

If you are giving your fish food that is rich in carbs or starch, this could lead to liver disease.

It would help if you tried not to provide them with cereal, bread, or pellets rich in carbohydrates so you can avoid any health-related issues and always choose healthier food options.

The Bottom Line

Fortunately, there are various treatment options for koi fish losing scales, given that you take immediate action.

A pro-tip to follow is to instantly quarantine your koi fish and move it to a separate tank to prevent the further spread of infection.

If your koi fish does not recover in a few days, you should take it to the vet immediately for further treatment. Best of luck!

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