How to Create a Koi Fish Pond in Your Australian Garden

Koi fish swim in the lake

A koi pond is a stress-beating and stylish addition to your garden. But to create a successful water feature, you need the right design and maintenance. Considering pond equipment, choice of aquatic plants, water quality, and protection from predators will all help you create the Australian koi pond of your dreams.

What You Need to Build a Koi Pond

Designing your koi pond and getting all the materials you need for it is the first step to a beautiful water feature in your garden. Be aware that the cost of installing a koi pond and maintaining it can run from hundreds to thousands of dollars, so plan a budget before you start.

Koi Pond Materials

Here's what you'll need to get started.

  • Stable soil - not too sandy or wet - in a setting with no more than four to five hours' sunlight; koi fish like a little sunlight but take comfort in shade
  • A space that is not directly under trees that drop leaves and twigs that dirty pond water
  • A smooth rubber pond liner that won't irritate the bellies of koi fish which tend to rest at the bottom of the pond when it's colder
  • A pressurised filter pump to filter fish waste and other debris
  • A water dechlorinator to remove chlorine and ammonia from tap water; active carbon can also be placed in your filter and used to continually clean the water for your fish
  • A koi fish pond skimmer that can house your pump and also catch debris
  • Koi carp and, possibly, their relatives - goldfish or other fish that can cohabitate with koi; prices for koi fish vary from around $20 to hundreds of dollars for each koi, depending on size, colour, vibrancy and markings, and well cared for, koi can live up to 40 years
  • Aquatic pond plants suited to a koi pond to help oxygenate the water, reduce algae, and provide shade for koi fish; water lilies do all three jobs and attract insects koi fish like to eat
  • Attractive rocks and stones to line the edge of the fishpond and perhaps some pond decorations or lights
  • A fountain or waterfall feature to further oxygenate the water
Beautiful pink waterlily or lotus flower in koi pond

How to Build Your Backyard Koi Pond

Now it's time to put your koi pond together. Allow at least a day and consider whether you need help from a landscape designer or an electrician.

  1. Dig a hole at least 1.5 metres deep for your koi pond, then line it with a flexible rubber liner. You could also use a prefabricated pond material, or have a smooth concrete base poured.
  2. Fill your koi pond with fresh, unchlorinated water. Chlorinated water, and the ammonia it often contains, is toxic to fish and will burn gills, scales, and breathing tissues.
  3. Place your aquatic plants and stones around the edge, as well as some pebbles and smooth rocks around the bottom of the pond. You can grow your plants in soil placed on the bottom of the pond too, or put them in pots for easier maintenance.
  4. Place your filter and aquatic pump, that will need to plug in to a power source, in the pond.
  5. Put your koi fish in, but not too many. To keep eight fish, you would need a pond at least three metres long, one to two metres wide and at least a metre deep.
  6. In a deeper pond, introduce one or two other fish such as goldfish, or the algae bloom-eating janitor fish or golden nugget plecos. Rainbow fish is another species that can live in harmony with koi, but experienced koi pond owners suggest one male rainbow fish only.
  7. Plants that control algae are also essential.

Maintaining Your Koi Fish Pond

Koi fish are very hardy, but being a koi keeper with a successful pond does involve committing to regular maintenance.

Water Temperature

Koi like the pond water to be around 20° C. If the temperature drops below 10° C during winter, you can invest in a pond heater, and also protect your fish by feeding them food that is easy to digest.

Oxygenation

Don't overcrowd your pond, check your filter, and use aquatic plants that photosynthesise under the water and remove carbon dioxide from the water and replace it with dissolved oxygen. A pond feature such as a waterfall will also ramp up oxygen levels.

Predators

Cane toads can lay eggs in your fishpond that are toxic to koi. Birds may also swoop on your pond. Placing a wire netting across the top of your pond will help protect your fish.

Cane Toad close up

Filtration

Your filter pump and aquatic plants will help filter waste. But, be wary of high ammonia levels after bacteria is broken down in the pond. Even low concentrations can kill your koi fish. You should do a weekly 10% water change. You can also add beneficial bacteria from an aquarium or pet shop to improve the water quality of your koi pond.

Feeding

Commercial koi food from an aquarium or pet shop is the easiest way to feed pond fish. Koi also enjoy cooked and salad vegetables and wholemeal bread.

What Are the Risks of Having a Koi Fish Pond?

Koi (Cyprinus rubrofuscus), which are closely related to the common carp (Cyprinus carpio), are an introduced species in Australia, not a native species. You'll only be allowed to keep them if you live in NSW or WA, and even then, only in a fully self-contained pond that does not connect to waterways.

Invasive Water Plant Species

For the koi pond owner, making sure not to buy or cultivate aquatic weeds is also important.

  • In Western Australia, aquatic plants that have been declared weeds include parrot's feather and leafy elodea, and these must be reported.
  • In NSW, alligator weed, Eurasian water milfoil, duckweed, and water poppy are all plants that are on the invasive species and aquatic weed list.
  • Water lettuce, Salvinia, and water hyacinth are on the banned list in both states.

Buying the right plant species from a reputable shop, and never putting invasive species in the green waste, is key. Always ask for native pond species, which will encourage frogs.

Koi Herpes Virus

Koi herpes virus (KHV) is fatal to koi. Always buy pond fish from a reputable dealer and ask if testing for KHV has been done.

Bring Beauty and Tranquility to Your Garden With a Koi Pond

While designing, building and maintaining a koi pond in Australia does require some planning and hard work, this water feature will reward you with colour, life and movement. Watching koi fish play in your pond is also a great way to increase mindfulness and reduce stress.

How to Create a Koi Fish Pond in Your Australian Garden