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FISH / new pets

A Set-Up Guide for New Koi Parents

Tips from home to health to food and fun.


What are koi?

Koi are a beautiful, colorful type of carp that can grow up to 36 inches long and live for 50 years or more. Koi are originally from Japan, but now are kept in ponds around the world. These beauties are omnivores who like plant and animal-matter food. Over time, koi learn to recognize their pet parents and can be trained to take food from your hand.

Introducing new koi to their home

Young koi can be kept in a large aquarium. Minimum aquarium size should be 29 gallons (110 L). With their large size and fast growth rate, mature koi should be kept in a large outdoor pond (at least 50 gallons (190 L) of water per koi).

They’ll thrive in a partly shaded, outdoor pond. If your koi are aquarium dwellers, they’ll do best in a quiet area, away from direct sunlight and drafts.

If you’re adding new koi to a tank, float them in the water — inside their bag — for about ten minutes. This will get them used to the water temperature in their new home before they start swimming.

Adding new koi to an existing school? Keep the new fish in a separate tank or pond for two to four weeks. This way you can make sure your new koi is healthy, before they mingle with other fish. On moving day, use a net to transfer them so old water doesn’t mingle with new water. Whether they live in a tank or a pond, add only one to three fish at a time.

Setting up your koi’s home

If your koi live in an aquarium, use a hood with light fixtures on top to reduce evaporation and splashing and to keep the more adventurous fish from leaping out. You’ll want to leave the light on for eight to twelve hours daily, so your koi can tell when its time to swim and time to sleep.

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  • Koi habitats need to be filtered to keep water clean. Look for a filter that’s the right size for a koi habitat.
  • You’ll need a filter that processes all the water in your tank three to five times per hour, or, for a pond, once an hour.
  • Add beneficial bacteria supplements to help break down waste in the habitat.
  • PetSmart offers free aquarium and pond water testing. Just bring in a sample of your aquarium water, and we can test the quality within minutes.
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Water temperature

Koi are pretty temperature-resistant— they can even hibernate under ice in winter. Just be sure your pond is at least three feet deep— otherwise, it could freeze solid, and koi aren’t that tough. When they live indoors, koi prefer cool water—between 65 and 75 degrees F (18 to 24 C).

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How to handle your pet

  • Always wash your hands with soap and water before (and after) handling your fish, their food, or tank; aquatic pets can carry bacteria, which can be passed to people.
  • Kids, pregnant women, older folks and people with immune system issues need to wash up with extra care and should avoid contact with pet waste.
  • Never keep pets near people food or the kitchen sink.
  • If you have to give up your aquatic pet, never set them free in the wild. They won’t adapt well and can damage natural habitats.

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