The Fundamentals of Koi

While koi are hardy and relatively easy to raise you must ensure their health by planning their pond environment carefully. Once the right pond is constructed, or refurbished, then and only then should you start the selection and acquisition of koi.

What a koi wants, what a koi needs

Water, lots of it

Koi can grow to quite a size. Their rate of growth and size at maturity could be up to 8 inches in length in their first year, and twelve to sixteen inches by the second year. Under ideal conditions they can grow up to thirty-six inches and weigh over forty-five pounds.

You should have a pond of at least 1,000 gallons with a smooth gravel substrate, rocks, and hearty plants. The pond should also be at least three to four feet deep. Also base the pond size to estimated mature size, not size at purchase.

The following chart estimates the number of fish each pond can support.

Typical Pond SizeSurface Square FtGallons at 3’ depthInches Supported21” koi supportedGallons at 4’ depthInches supported21” koi supported
6 x 8481077108514361447
9 x 98118171828242324211
9 x 12108242324211323232315
9 x 16144323232315430843120

Cold protection

While a koi can tolerate the cold, and have been bred to survive brief, cold winters, they will still need time to adjust to variations in temperature. This is why you will still need to pay attention to their needs pertaining to their handling.

You will need at least a 3-4 foot deep pond so that when there is a 6-8 inch thick ice over it during winter there is substantial gas exchange of surface water. You will have to provide this surface with a bubbler to circulate the water and prevent freezing in cool climates. You can also use a de-icer for colder climate.

Old Age and Companionship

Koi can live up to an average of between twenty-five and thirty-five years. You will need to be ready to literally commit to your koi. This will include moving them with you when you relocate. Koi can recognize their owners, and are sociable creatures by nature.


Also provide enough oxygen to your koi. You can consider adding a waterfall or fountain to your pond. You can also add a venturi that will properly aerate your pond.

Over summer the amount of waste will increase. You must make sure that you increase the oxygen levels and do partial water change if the water is tested high for ammonia and nitrate.


No one wants to live in a dirty habitat. Koi included. Provide substantial mechanical and biological filtration to maintain proper water conditions. There are many types of filtration systems and media that you can purchase these days in the market. Choose the ones that suit your pond best.

Good food, good life?

A good diet

Provide food pellet or flake food with seasonally available mix of wheat germ, protein, fruits, vegetables, plankton, shrimp, and color enhancing foods.

Color enhancing foods contain ingredients like spirulina and carotene, and are fed to bring out the brilliance of koi. Adversely enough, the use of these products itself may cause the white areas of the fish to turn orange/yellow. Alternate the use of colour enhancing food with other diets to maintain the white brilliance.

Careful feeding

Do not overfeed your koi. Feeding it excessively isn’t going to make it grow faster.

The only thing you will gain by over feeding is an overload of nutrients in the pond. This can lead to problems including excessive algae and poor water quality.

Do not feed koi when the water temperature dips below an average of 50 degrees. This can cause indigestion to your koi.

Plants and natural pond foods

Koi are omnivorous and will feed on pond plants. These plants would have been placed there to create oxygen, and provide shade to cool the water and protect the koi. You should construct a barrier of stone, large rocks etc. to protect the plants.

Also remember that koi feed on certain algae to enhance their own colour. Do not wipe out algae populations with controls like copper sulphate. Keep algae at acceptable levels by making selective use of products like Algae Fix, or natural controls, like barley straw.

Loi also feed on mosquito larvae, thus controlling mosquitoes.

Protection from predators

Always protect your koi from predators.