Keeping Koi

Keeping Koi

This fact sheet is not intended to provide a complete guide to keeping Koi, there are many online resources already in existance for this purpose. However, much literature is written by breeders and keepers of show quality Koi. A large number of Koi owners have smaller back yard ponds and gain great enjoyment from keeping Koi that are not show quality. Not everyone can afford gigantic ponds with top of the line filtration systems for their Koi, it is possible to successfully keep Koi in smaller systems.

Contrary to things you may have read, keeping Koi is not difficult. Koi are hardy, fast growing fish that come in an endless range of colour and pattern combinations. The two basic requirements for healthy Koi are good oxygenation and good filtration, if these two components are right in your pond system you will gain many, many years of enjoyment from your Koi.


Pond depth

Often books and articles that discuss keeping Koi are written for cold climates where it is necessary to have deep ponds so that Koi can survive long winters, we do not have this problem in most areas of Australia. At Swan Valley Fish and Lily Farm we run all our Koi in 30-40cm deep ponds and we have many happy customers doing the same. Western Australia’s strict swimming pool regulations make shallow ponds the only option for most people. There are many strange claims about Koi growth and body shape in relation to pond depth that appear to have no basis in fact. We have thousands of Koi at Swan Valley Fish and Lily Farm and plenty of them have grown from fry to 65cm in our shallow ponds. There are many advantages to having a shallow pond such as ease of maintenance, improved safety for children and pets, reduced chance of there being anaerobic bacteria and last but not least ease of viewing your beautiful fish.


Koi nutrition

There are many types and quality levels of food suitable for Koi. If your budget allows there are super high protein feeds with superior colour enhancing ingredients. These foods produce optimum growth of Koi, which may be important if you are wanting your Koi to grow to it's full genetic potential. However, large fish can become costly to feed and many people with Koi, that are not show quality, choose to use a more economical feed product. These products still contain the nutrients required to maintain good fish health, they may not have the same colour enhancement capabilities and protein levels will be less. Often people choose to mix different quality Koi foods together to gain some of the benefits of the more expensive foods. Koi also enjoy additional treats such as roast pumpkin, lettuce and watermelon. Do not give your Koi meat or dairy products.


It is important not to over feed your Koi. Only feed what the Koi will eat within 5 minutes, if food remains in the pond after this time it should be removed, ensure you give less food next time you feed. Over feeding will ultimatley lead to a green unhealthy pond for your fish, reducing life expectancy. Small frequent feeds are best if you wish to maximise Koi growth.


In warmer climates such as Perth and many other locations in Australia (where Koi are allowed to be kept) it is possible to feed Koi all year round. However, it is recommended that you reduce the quantity and frequency of feed in the cooler months, many Koi owners opt for a lower protein feed during these times. In colder climates it may be necessary to cease feeding completely. Koi will generally become disinterested in feed when the water temperature falls too low. There are many good resources with regards to managing Koi feeding in colder climates, this is an area where we do not have a lot of experience, as our Koi are still chasing us up and down the ponds in the middle of winter as our water rarely falls below about 15 degrees.


Koi behaviour

Moving to a new pond is a very stressful time for Koi, differences in water quality, temperature, pH etc can effect their health so it is important to watch for signs of illness. Koi may take a while to adjust to changes to food type and may initially refuse to eat any new foods they are given. 

In the first few weeks after introduction to a new pond, Koi are often skittish, hiding away and refusing to come out for a feed until you have moved away from the pond. This behaviour is particularly likely in ponds with no other fish, if there are existing Koi in the pond, the new Koi will join the others and their nervous behaviour disappears quite rapidly. As your Koi become accustomed to their new surroundings, they will become more confident and will soon be coming out to greet you for a feed every time you approach the pond.

If you are still not seeing much of your Koi after a couple of weeks then it may be for one or more of the following reasons:

  • A predator approaching the pond while you are not there - ie birds, cats or other animals
  • Too few fish in the pond. Often increasing the number of Koi in the pond will make them all more vigorous and bold. 
  • Deteriorating health due to poor water quaility or disease.

When you feed your Koi you will get to know their normal behaviours and will soon notice anything untoward. Behaviours you should be particularly concerned about include:

  • Refusing to feed
  • Gasping at the water surface 
  • Remaining motionless in the pond - either at the surface or on the bottom of the pond
  • Rubbing their bodies against the walls of the pond or other items in the pond
  • A single Koi removing itself from the rest of the group 
  • Fins clamped

Additionally you should look at your Koi for any physical abnormalities such as lesions, discolourations or protrusions as these could be a sign of parasitic, fungal or bacterial infections. 

For further reference there are many good online resources and books that have pictures of various diseases that afflict Koi and the best way to treat these diseases. This book "Manual of Koi Health" is quite good. When choosing a product to treat Koi disease, we recommend you select one that does not require water changes. Many "all natural" products contain oils that build up in the pond, these products may be suitable for small aquariums but it is hard to justify their use when we have such a shortage of water.


Stocking rates

We can not stress enough how important filtration and aeration are with regards to stocking rate in your pond. As a good general guide a lightly stocked pond with the water being turned over every hour to an hour and half would have 1Kg of Koi per 1000 litres. A heavily stocked pond would have around 3kg of Koi per 1000 litres. If you have a heavily stocked pond then you should try to turn all of your water over about twice an hour.

Here is a calculator that can help you estimate the weight of Koi, so you can gauge what your stocking rate might be.