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Koi Care Sheet

Developed with and approved by a qualified veterinarian.

Koi fish

This care sheet covers a variety of koi including:


Cyprinus carpio  

Koi is the common name for the ornamental-colored variants of a species of carp. Koi have been a popular fish in Japan for generations. Koi were the first fish species successfully bred in captivity on a large scale. Koi can grow quite large and their beauty is impressive.

Typical appearance and behavior

  • Create more waste than other fish of comparable size and require better filtration
  • Color patterns on multicolored koi may change throughout lifetime; will often lose black markings as they grow


Care Difficulty Intermediate to advanced
Average Life Span Up to 50+ years with proper care
Average Adult Size Up to 3 feet long, depending on species
Diet Omnivore
Minimum Habitat Size 29+ gallons, for juveniles
Water Temperature 64-75°F


Habitat size

Keep in an appropriate size aquarium or pond based on the adult size of the species selected. A minimum of 29 gallons is recommended for the health and wellbeing of juvenile koi. A general rule of thumb is 5 gallons per every 1 inch of an adult koi’s length.


Building your habitat

Koi prefer a cooler environment and are not recommended for tropical aquariums

  • Water health - Provide proper filtration to ensure optimal water quality to help maintain health. Slow water circulation should be provided to mimic water currents and high oxygen levels found in the koi’s natural habitat. Stable water quality (pH, ammonia, nitrate, nitrite) and water temperature are critical to the health of aquatic life. If you are unsure of your water quality, bring a sample to Petco for free testing. Ensure water temperature does not fluctuate more than +/-2 degrees in either direction in a 24-hour period  
  • Décor- Koi can grow large. Provide some rocks and hiding places, but leave plenty of open areas for swimming


A well-balanced koi diet consists of:

  • Flakes, pellets, frozen or freeze-dried foods
  • Koi need more carbohydrates than other freshwater fish; feed them foods specifically formulated for koi

Things to remember when feeding your koi:

  • Feed small amounts once a day, only as much as they can consume in 1 to 2 minutes
  • Thaw frozen foods before feeding
  • Koi are opportunistic feeders and will continue to eat if offered food. Overfeeding can be detrimental to their health and cause higher waste production
  • Koi are voracious eaters. Feeding a sinking diet will help prevent excessive air consumption while eating.


Koi care

  • Water care - Maintaining great water quality with regular water changes and adequate filtration is important to help keep your koi healthy
    • Daily: Check filter, water temperature and other equipment
    • Weekly: Test water quality at least once a week
    • Weekly to monthly: Change 10 to 25 percent of the total volume of water every two to four weeks, or as needed. Change filter media monthly
  • Avoid overcrowded conditions, as this is a major cause of stress and disease

Where to buy koi

 Various koi are available for purchase at your local Petco Pet Care Center. Please call ahead to check availability.


Tank mates

Compatible with cold-water community fish who can tolerate lower temperatures. Can be kept singly or in schools if tank or pond is large enough. Some species that may do well with koi include high-fin banded shark, shubunkin and comets. 


Signs of a healthy koi

  • Clear eyes
  • Healthy appetite
  • Active swimming
  • Regular breathing
  • Free of parasites or disease


Red flags (If you notice any of these signs, contact your local aquatic specialist or veterinarian.)

  • Loss of appetite
  • Loss of color
  • Spots or fungus on body or mouth
  • Labored breathing
  • Listlessness
  • Cloudy eyes or pop-eye
  • Elevates scales
  • Frayed or discolored fins
  • Erratic or trouble swimming
  • Weight loss
  • Bloating

Common health issues

Health Issue Symptoms or Causes Suggested Action
Health IssueFungus Symptoms or CausesWhite cottony growth and/or discoloration of the eyes. Suggested ActionQuarantine fish; use a commercial antifungal remedy. Consult your local aquatic specialist or aquatic veterinarian.
Health IssueIch Symptoms or CausesWhite spots appear on fins and body; fish rubs against hard objects or swims erratically. Rapid respiration. Suggested ActionQuarantine fish immediately; add freshwater salt and use commercial ich remedy as directed. Consult your local aquatic specialist or aquatic veterinarian.
Health IssueBacterial infections Symptoms or CausesCloudy eyes, open sores and/or reddening of the skin. Suggested ActionImprove water quality; use a commercial antibacterial remedy as directed; consult your local aquatic specialist or aquatic veterinarian for treatment.
Health IssueFin rot Symptoms or CausesFrayed or disintegrating fins; the base of the fins usually reddens. Suggested ActionImprove water quality. Consult your local aquatic specialist or aquatic veterinarian for treatment.


  • How long do koi fish live? With proper care, koi can live an average of 50+ years.
  • What do koi fish eat? Koi should be offered a variety of flakes, pellets, freeze-dried and frozen food. A koi-specific, higher carbohydrate diet is best.
  • Is a koi a carp? Koi are members of the Cyprinid family, a colorful, domesticated variant of carp.
  • How do you build a koi pond? A pond can be built from various materials from preformed plastic molds to holes dug in the ground and utilizing a pond liner.
  • Where can you buy koi fish? Various koi types are offered in Petco Pet Care Centers. Call ahead for availability.
  • What are koi? Koi are large, colorful, domesticated carp.
  • How fast do koi grow? Koi grow quickly and can reach a size of 6 to 8 inches long within their first year of their life.
  • How deep should a koi pond be? Ponds that are in warm climates should be at least 3 feet deep. A minimum of 4 feet is needed in regions that experience freezing.
  • How do you take care of koi fish? Koi can grow large quickly. A properly set up and filtered aquarium or pond should be provided. A minimum of 29 gallons of water is needed for a juvenile koi.
  • How big do koi fish get? Koi can obtain a length of up to 3 feet, depending on the species.
  • What should you feed koi fish? Koi should be offered a variety of flakes, pellets, freeze-dried and frozen food. A koi-specific, higher carbohydrate diet is best.

Additional care sheets

Notes and resources

Ask a Pet Care Center associate about Petco's selection of products available for the care and happiness of your new pet. All products carry a 100% money-back guarantee.

Because all aquatic life are potential carriers of infectious diseases such as atypical mycobacterium and salmonella, always wash your hands before and after handling your aquatic life and/or habitat contents to help prevent the potential spread of diseases.


Pregnant women, children under the age of 5 and people with weakened immune systems should contact their physician before purchasing and/or caring for aquatic life and should consider not having aquatic life as a pet.

Go to the Centers for Disease Control at for more information about aquatic life and disease.

The information on this Care Sheet is not a substitute for veterinary care. If you need additional information, please contact your veterinarian as appropriate.