Why Are My Koi Not Eating? (With 5 Easy Solutions)

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I remember the first time I noticed something amiss in the koi pond. Two of my favorites had been swimming around, although I had not seen them eat anything. As time passed, I learned what may cause appetite changes in koi fish and how it is solved.

Koi fish typically stop eating when the environmental temperature drops. That causes the fish’s metabolism rate to decrease, and therefore, the fish will eat less. However, koi fish also stop eating when they don’t get enough oxygen, when carrying a disease, or when the water parameters are wrong.

As we move forward, I wish to share five common reasons why koi fish stop eating. I will provide you with some easy solutions as well. In short, that includes testing the water parameters using dedicated kits and oxygenating the water with a high-end air stone.

Why Are My Koi Not Eating?

Koi fish are similar to other species. You have to feed them once or twice a day, and in quantities, they can finish in two or three minutes. But if your koi fish have refused to eat, you have to act because some of the factors that cause koi fish to lose their appetite are serious, including:

1. The Temperature Declines

If your koi fish live in a pond, which is often the case, the temperature will alter their feeding habits. Koi fish eat a lot in the summer and spring because the temperatures during these seasons range between 68 and 86 degrees F. You can feed the koi fish twice a day. In fact, smaller Koi can eat up to four times a day.

But when the temperature drops past 68 degrees, the Koi’s digestive system will slow down. It won’t eat as much food. If the temperature falls to 50 degrees, the Koi will eat even less. You can still feed it twice a day, but you have to reduce the quantities because, at that stage, the Koi need very little food to survive.

Once the temperature drops below 50 degrees, the Koi will eat two, maybe three times a week. That is two or three times weekly, not daily. At 41 degrees, the Koi will enter hibernation. At this point, it will stop eating entirely.^[1]

2. Your Koi Live In An Ecosystem Pond

Ecosystem ponds require very little maintenance. They consist of water, mechanical filters, biological filters, aquatic plants, algae, rocks, gravel, and pond animals like frogs, turtles, birds, and fish.^[2]

Ecosystem ponds are not necessarily self-sustaining. But if you configure yours correctly, it can survive without regular water changes and pH or temperature tests. More importantly, you can get away with feeding a koi fish in an ecosystem pond once or twice a week.^[3]

The fact that they can survive for so many days without external food sources is a good thing. Don’t take it as a sign of trouble. The koi fish are still eating regularly. In an ecosystem pond, they can survive on plants, worms, insects, and algae.

3. The Koi Fish Aren’t Getting Enough Oxygen

Oxygen deficiencies can compromise a koi’s appetite. This is true for other animals, including humans. If you can’t breathe, you won’t eat.

In a pond, a storm can reduce the oxygen content in the water.^[4] Many aquarists respond by giving the koi fish less food because they know that they don’t have enough oxygen to digest food.

4. Your Koi Are Carrying A Disease

Loss of appetite is one of the most common signs of illness in fish. Koi fish are susceptible to various diseases, including anchor worms, dropsy, costia, flukes, and fin rot.

Sick or stressed koi fish will gasp for air at the surface. They may also rub against objects. In some situations, their colors will become dull. Over time, as their appetite deteriorates, they will become inactive.

Severe injuries produce similar results. Sick or injured koi fish may spend weeks at a time in hiding, either occasionally emerging for food or ignoring the food altogether.^[5] Some koi fish will recover on their own. But others will become sicker until you intervene or they die.

5. The Water Conditions Are Bad For Koi

If two or three koi fish have lost their appetite, you can look for signs of disease, stress, injury, or even poor nutrition. But if most or all the koi fish have stopped eating, you should investigate the water conditions.

A poorly maintained environment with the wrong parameters can affect all the koi fish in the water, lowering their appetite and making the creatures less active. Test the water for toxins like ammonia. Better yet, make sure the tank is cycled. Poor water conditions can kill your entire population of koi fish.

How To Treat Koi Fish That Stopped Eating?

If the koi fish stopped eating because it entered hibernation due to a drop in the temperature, you don’t have to do anything. But if the fish is not in hibernation, you can take the following steps to prevent the creatures from starving to death:

1. Adjust The Water Parameters

These are the best water parameters for koi fish:^[6]

Temperature: 74-86 degrees F (23-30 degrees Celsius)
Water pH: 6-9.
Water hardness: 9-18 degrees dH.
Ammonia and nitrites: 0 ppm.
Nitrates: <20 ppm.

If your Koi are not eating, start by improving the conditions in the fish’s environment. To measure the pH, ammonia, nitrates, and nitrites, I personally use API Water Test Kit (link to Amazon). Within a few minutes, this bundle will indicate if there is something wrong with your water.

If the pH is too low or the ammonia is too high, I suggest performing more frequent water changes. You should also remove leftovers that got rotten. These will make the water acidic and compromise the Koi’s health.

Bear in mind that Koi fish require at least 250 gallons of water. They are more likely to thrive in ponds because ponds provide ample room for the fish to explore. Two hundred fifty gallons sounds like a lot of water, but some koi fish are so large you have to keep them in 1000 gallons.

No one will stop you from maintaining koi fish in an aquarium if you find one of sufficient size. But a pond makes more sense, preferably one with a depth of at least 6 feet. I also suggest adding plants like cattails, duckweed, water hyacinth, and pickerels to alleviate stress.

2. Identify And Treat Sick Koi Fish

If you suspect that your Koi is sick, I suggest placing it in quarantine. This protects the fish’s healthy neighbors from infections. Once you place the sick fish in quarantine, you can apply broad-spectrum treatments.^[7]

Here is an excellent Youtube video that demonstrates some common koi fish diseases and ways to treat them:

In extreme circumstances, you have to treat the entire pond, especially if the water is infested with worms and parasites large enough to see. Clean the pond thoroughly to prevent the diseases and infections from recurring.

Some people treat their ponds with a wide range of antibacterial and anti-parasitic treatments twice a year. If you don’t have the time for routine treatments, check your skimmers and filters. Are they still functional? What about the pumps? Has the water grown stagnant?

Ask a professional to analyze your setup. Let them look at your hardware. They can determine whether or not the filters and pumps are powerful enough to meet the needs of your pond.

To protect old koi fish from bacteria and parasites, ensure you quarantine new fish.^[8] Observe them for two to three weeks. If they haven’t developed any concerning symptoms by the end of this period, you can acclimate them before moving the creatures to the main tank/pond.

3. Create A Routine Feeding Schedule

I highly recommend creating a feeding routine for your koi fish. If you feed your koi fish twice a day, add food to their pond at the same time every single day. This will train them to expect food during those moments.

It will also teach them to eat at the same time every day, even when disease and stress overwhelm them. Try to create a situation where your koi fish rise to the surface whenever they see you.

If you can get them to eat food out of your hand, as some aquarists do, you can force them to eat even when they don’t have an appetite. But don’t overfeed the fish. Give the Koi what they can finish in three minutes.

Overfeeding will make them sick, although underfeeding is just as problematic. Install an automatic feeder if you’re too busy to place the fish on a regular feeding schedule.

You can’t do anything for koi fish that enter hibernation mode. They don’t need food until spring. That being said, before the koi fish enter hibernation, you have to cut back on the amount of food you add to their water.

If the koi fish enter hibernation with food in their stomach, that food will rot, resulting in a potentially fatal bacterial infection. Once temperatures reach 41 degrees, you can stop feeding them. Don’t add any more food to the water until spring, even when the koi fish ask for it.

4. Oxygenate The Water

As was mentioned earlier, cloudy weather and strong winds can cause oxygen deficiencies in ponds. That can also be the case if some of your plants have died or if your pond lost large amounts of algae.

By creating aeration and bubbles, you can improve the oxygen levels in your tank within minutes. That is where I typically recommend the Pawfly Aquarium 8 Inch Air Stone (link to Amazon). It also works great in aquariums, in case you are using one for your Koi.

5. Improve The Food Quality

Some koi fish stop eating because they are bored with their meals. Others do not appreciate the quality of the food you keep adding to the pond. You can solve this issue by either changing brands or improving the food quality.

Look for brands with a high concentration of vitamins and proteins. Try to vary their food. Rather than giving them flakes and pellets every single day, experiment with silkworms, mealworms, shrimp, etc.

I personally recommend the Blue Ridge Floating Pellets (link to Amazon). This food contains an excellent combination of protein, vitamins, and carbohydrates. It is likely to encourage your Koi to eat and provide them with some intense, beautiful colors.

A happy koi fish in a clean well-oxygenated environment that has plenty of high-quality food will eat regularly and in healthy amounts.^[9] Even if the koi fish stops eating because of injuries, a clean tank with regular nutritious meals will enhance the creature’s recovery rate, eventually restoring the koi fish’s appetite.

How Long Can Koi Fish Go Without Food?

During the summer, when conditions are optimal, the koi fish can survive for two weeks without food. This applies to other pond fish. They may persist for more extended periods if their environment has alternative food sources like algae and plants.

So generally, the time koi fish can go without food depends on the weather and the conditions in the tank. The digestive system of a koi fish fluctuates with the temperature. When the temperature rises, a koi fish’s metabolism will increase.

The fish will eat two, three, four, or even five times a day. But if the temperature exceeds 95 degrees, the creature will stop eating because it is not accustomed to temperatures within that range. It will attempt to conserve energy.

If the temperature falls, the koi fish’s digestive processes will slow down, reducing the amount of food it needs to survive. At 40 degrees, the koi fish will stop eating as it enters hibernation.^[10]

During this period, it can survive without food for weeks. During the winter, the koi fish won’t eat. They can’t digest food at such low temperatures.

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Conclusions

Koi fish usually stop eating due to stress, disease, or changes in the water quality and temperature. When this happens, feeding them won’t do you any good. Even if they eat for a couple of days, that food may rot in their stomachs.

If you designed your pond correctly, you should be able to prevent your koi fish from getting sick in the first place. However, it is essential to check the state of your water quality on a regular basis.

If cold temperature causes the issue, you are not required to do anything. That is a natural process the fish enters toward hibernation. All you can do is to see if the rest of the parameters are correct and that the fish gets enough oxygen. It is also crucial to see if the fish presents any signs of illness.