Essential Tips for Keeping Koi Fish as Pets

In recent years, koi fish have gained immense popularity as outdoor pets due to their vibrant colors and big personalities. In Japanese culture, these fish represent prosperity and good fortune.

If you’re considering adding one to your home, you’ve come to the right place. While keeping a koi fish can be tricky for first-time fish parents, this blog can help you make the process easier.

Koi fish can grow up to 36 inches long, depending on the species, and with the right care, can live for as long as 50 years.

There are over 20 koi fish types, each with its own distinguishable physical characteristics. The most popular ones are Kohaku, Sanke, and Showa.

These ornamental fish are playful and engage with their owners by swimming close to the surface, showing off their colors and patterns.
Whether you install a fish pond or keep them in an aquarium, you will need plenty of supplies to keep these creatures healthy and happy.
Here’s a list of essential supplies you will need:

  • Aquarium or Pond
  • Dry and frozen food
  • Accessories
  • Water conditioner
  • Water Filter
  • Water test kit
  • Full-spectrum lighting
  • Soft mesh net
  • Thermometer
  • Freshwater substrate
  • Refractometer
  • Aeration systems (Airstone and Air pump)
  • Check valve
  • Freshwater salt

Appropriate supplies allow you to care for your fish in the best way possible

Why is an Aeration System Necessary?

The aeration system is a device or method that adds oxygen to the water and improves its circulation. This system is important for fish because it helps them breathe, maintain their health, and prevent diseases.

Koi fish are large and produce a lot of waste, which can lower the oxygen level and increase the ammonia level in the water. Aeration systems can prevent this by increasing the dissolved oxygen content and enhancing the biological filtration of waste.

Several types of aeration systems can be used for tanks or ponds, such as air stones, filters, waterfalls, fountains, or diffusers. The aeration system can also create a more natural and attractive environment for koi fish by creating bubbles, currents, or sounds.

How to Care for a Koi?

Keeping Koi fish at home becomes easier when you understand how to care for them. Below are a few things you must remember before you bring a koi home.

Koi fish are sensitive and, therefore, easily impacted by external elements. Whether you keep your fish in a pond or aquarium, ensure it is spacious.
Since koi fish grow quite large, the aquarium must be big enough to accommodate all the fish at their maximum length and the waste they produce.
The aquarium should be placed in an area without exposure to direct sunlight.

If you keep your koi in a pond, ensure it’s at least three feet deep and that there is a minimum of 250 gallons of water for each koi fish. The deeper the pond, the safer your fish will be from predators. You can add a net to keep your koi safe, but it will compromise the aesthetics of the pond.

Deeper ponds are also great during the winter as they keep the water from freezing over.

Note: We advise you to quarantine new fish in a separate enclosure before adding them to the pond. This will allow you to monitor their health.

Water specifications:

A key factor affecting your koi’s well-being is the water quality within the enclosure and its parameters like temperature, pH, and the presence of ammonia, nitrite, and nitrate.

  • Temperature: For indoor fish, the ideal temperature is 64-75°F. Use a thermometer to check and maintain the temperature, ensuring it doesn’t fluctuate more than +/- 2 degrees.

Koi fish can survive in cold water; however, if kept in a pond, add de-icers to prevent the water from freezing completely during the winter.

  • pH: To keep your koi happy and healthy, the pH levels should be between 7 and 8.6. Higher or lower pH can be extremely harmful and even fatal. You can use test kits to check the pH levels. If the pH is lower, add baking soda to increase the level, and in case of a higher pH reading, add fresh water to neutralize it.

You can download the PetMyPal app to connect with a licensed vet using our vet chat feature for further assistance. This app is great for non-emergency situations where you can chat virtually with a veterinarian from your home.

  • Ammonia: This is highly toxic for koi fish. It is important to change the water frequently and use ammonia removers.
  • Nitrate and nitrite: A high level of nitrate or nitrite in water is dangerous for koi fish. 20-60 ppm is safe for this marine life, but higher amounts should be avoided.

Use test kits to check nitrate and nitrite levels, add plants and aeration systems, and change the water daily.

  • Filtration: Since these fish produce more waste than their counterparts of the same size, keeping the water clean and fresh is essential.High-quality filtration systems can help keep the water clean and free of toxins.

Decor not only helps enhance the aesthetics of your aquarium or pond but also mimics the natural habitat of marine creatures. Remember that any decor you choose must accommodate their growing size. 

If you have a pond, you can add a variety of plants, such as water lilies, water irises, lotus plants, and many more, to add beauty and offer shade.


A high-quality, well-balanced diet is paramount to keeping your koi fish healthy. As omnivores, these fish consume both plants and meat-based foods, like worms and insects. Domesticated koi require a diet that is low-fat and rich in protein. Feed your pet fish food that is specially formulated for koi fish to make sure that they are getting all the essential nutrients needed.

Don’t overfeed your koi. For indoor fish kept in an aquarium, once a day works fine. If you keep your koi in a pond, you can feed them up to 4 times a day, but just enough that they can finish all the food in under 2 minutes.

Their diet will change with the seasons. Like some animals in hibernation, koi fish rarely eat in the winter.

Besides formulated fish food, you can add fruits and vegetables to your koi’s diet.

Here’s a list of items that are safe for koi to munch on:

  • Orange slices
  • Grapes
  • Watermelon
  • Garlic
  • Broccoli
  • Lettuce
  • Crayfish
  • Bloodworms
  • Cooked shrimp

Avoid feeding your koi peas, corn, white bread, or anything that contains carbohydrates, as they have trouble digesting such food.

As a pet parent, you will have to learn how to balance your koi’s diet according to their changing nutritional requirements with the change in weather.

Keep in mind that fish are very sensitive and need extra care. Speak to your vet before adding or making any changes to their diet.

Common health issues:

Caring for fish becomes easier when you know the dangers your pet may face. Koi are susceptible to the following:

  • Parasites: Ich, Fish lice, Trichodina, Chilodonella, and Costia are all parasites prevalent among koi fish. Your koi may have white spots and experience rapid breathing. Quarantine the victim, add aquarium salt, and contact your vet for treatment immediately.
  • Bacterial infections: Dropsy, fin rot, and ulcers are caused by harmful bacteria. Check for cloudy eyes and seek antibacterial treatment.
  • Fungus: Another common disease that requires you to isolate the affected fish. Look out for discolored eyes and cotton-like growth.
  • Other prevalent illnesses in koi fish include flukes, anchor worms, and ammonia poisoning. We have shared some symptoms you must watch to know when to contact your vet.

Signs of diseases:

  • Fins appear closer to the body
  • Gasping at the surface or breathlessness
  • Discoloration
  • Rubbing its body on objects
  • Different or bizarre swimming
  • Swollen abdomen
  • Low appetite

These signs indicate that your koi is suffering from a disease or infection. Visiting your vet is a must to get your fish treated properly. These diseases can be prevented by maintaining water quality and cleanliness and offering a nutritional diet.

Quarantine each new fish you get to ensure that the fish is not the carrier of any diseases. Illnesses can be transferred from these aquatic pets to humans, so take caution by washing your hands after every interaction.

Koi fish are stunning creatures and are thought to bring luck into the lives of their owners. We hope this blog has helped teach you how to prepare and care for your koi. Good luck!

Adam Hill

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