On Sunday 30 May, 2021, NSW’s two koi clubs, the Australian Koi Association and the Koi Society of Australia are holding their combined annual koi show at the Sydney International Equestrian Centre, Horsley Park in Sydney’s western suburbs from 9am-3pm.

At the “Easter Show” of koi exhibition and competition in NSW, internationally accredited koi judges will select champions across a large range of koi varieties, as well as grand champion and other outstanding awards.  Anyone curious about seeing the very best koi in NSW, will find no better opportunity than to spend a few hours looking at the hundreds of fish on display.

I’ve kept koi in our backyard pond for 21 years. Friends who come to our place are often spellbound by the beauty of what we have developed over the years. They tend to ask very similar questions about what’s involved in keeping koi, the costs, the problems as well as the sheepish perennials:  do I give them names like cats and dogs (no), and do I ever eat them (no, but carp are one of the most eaten fresh water fish in the world, particularly in Eastern Europe).

With the show coming up, I thought I’d set out to answer questions I am most often asked about keeping koi.

How did you build your pond?

When my father Alec died in 1999 at 89, my share of his estate was just $26,000. Instead of just paying a soon-to-be-forgotten tranche off our mortgage, we decided to landscape our garden with a koi pond in his memory. We’d been mesmerized by one in a garden shop in Terry Hills which had been made in a Japanese style, with wooden bridges, large rocks, stone lanterns and a waterfall. It was unforgettably beautiful.

With our kids, we spent a couple of weekends digging out a large hole, and piling the soil at one end against a brick wall to create a mound on which to create a waterfall that would cascade into the pond. After about half a metre we struck our sewage pipes, so that defined the maximum depth of the pond we could build.  Most ponds are deeper than ours, with many converting unwanted swimming pools.

There were three choices of pond liner in which the water sits: concrete, moulded fibreglass or a thick rubber sheet liner, cut to size to cover the floor of the pond, its sides and an overlap above the sides that would be anchored with rocks and soil. We went with the easiest option with the rubber and 21 years later it’s never sprung a leak.

A landscaper who’d never built a pond before but who came highly recommended fitted the rubber, landscaped the surrounds and the waterfall and constructed the essential filtration system that, driven by a 400watt 0.5 horsepower pool pump recycles water from the pond through a 250 litre bioball filter  and back into the water, oxygenating it via the waterfall and a venturi. You cannot keep koi successfully in water that is not oxygenated nor filtered. Don’t even think about it. And keeping koi in an aquarium tank is both cruel and something that will be short-lived as they rapidly grow too big.

What did the pond cost to build and run?

Our pond has a very irregular shape, so its precise dimensions are hard to give accurately. My estimate is that it’s about 5000-6000 litres. 21 years ago, the combined cost of the large rubber pond liner, the biofilter, pump, four large fake fibreglass “rocks” on the waterfall that channel four water outlets into the pond, perhaps 2 tonnes of bush rocks, all the filter plumbing and plant landscaping around the pond and the labour was about $24,000. The required childproof fencing in glass was another $4000.

Most koi keepers run their filtration systems 24x7x365, so there is always the electricity cost of that which will depend on the size of your pond and pump. I have a timer on my pump which I set off during the peak electricity period (3pm-9pm) to save cost.  During that time a timer turns on an 80w aerator ($100) which sends air bubbles to three points in the pond.  We have a 5kw solar rooftop system on the roof which has reduced our total electricity bill, pond included, from about $2400 to $700 per year.

We direct rainwater runoff from the back of our house into the pond which saves on water top-up costs. It’s important to do periodic partial water changes to ensure water quality. That adds some cost, but I’ve never fainted on seeing our water bill.

There are also not very expensive costs involved in buying water quality testing chemicals for issues like PH, ammonia and nitrates. If water becomes too acidic, this is easily rectified by throwing in liberal quantities of bicarbonated soda. A 25kg bag can be bought for $33 from agricultural suppliers.

Food costs

The staple food I feed our koi is protein pellets. I buy a 25kg bag about twice a year from a contact who sources it from a wholesaler who sells it principally to commercial fish farms. I pay $120 per bag.  Koi are voracious eaters in summer, but eat perhaps 10% of their summer feed during colder winter months when they tend to slow down and are not as active in the pond.

Food at reasonable prices is sold at the koi auctions. But I never buy food from pet shops, eBay or even online so-called bulk suppliers where quite extortionate prices are charged for small packages.

I supplement the pellets with worms from our worm farm, maggots from the compost bin, stale bread, garden snails and slugs (we never use poisons), and left over cooked rice. In summer, throwing any of this in the pond causes piranha-like frenzied feeding. They also nibble algae from the sides of the pond and rocks and eat any mosquito larvae which find their way into the water.

Where can you buy koi in NSW?

I get my koi exclusively from two sources: koi auctions held 10 months of each year by rotation between the two clubs. Since March this year they have been held at Fairfield Showground on the Saturdays shown on the two clubs’ websites (links earlier in this blog).

About 125 bins containing either single or multiple koi are sold at each auction. Prices vary enormously according to quality and whether a particular bin attracts bidders willing to keep the price rising. The most expensive fish I’ve ever seen sold went for $2400 (to gasps and cheers) and the cheapest for $20. At each auction, there’s usually a few bins that go for over $500, but the great majority sell from about $70-$400. I’ve never seen a bin fail to sell. Even the ugliest of fish that only a mother could love will sell. “Catfood” is sometimes heard whispered.

Many koi keepers put word out to other collectors that they are looking for a particular variety. Word filters back that someone has a variety that you are looking for, particularly six months after a breeding session has produced hundreds of fish that can’t be kept by the breeder. I’ve acquired some of my best fish this way.


Female koi spawn in Spring, and there’s lots of folklore among breeders about when you can predict the exact spawning period will be. Moon phases, water and air temperature and storms are some of the factors you hear people swear by. Just as happens with horse, dog and cat breeders, koi breeders plan which variety pairings they will try to get together.

Not all who keep koi breed them. My impression is that most do not because to do so, you need a “bridal suite” tank where the selected male and female are placed together in the for a week or so in the hope that they will  get to know one another. After spawning and fertilisation by the ardent male, the two adult fish are then removed. The fertilized eggs cling to simulated water plants (mop heads are often used) and then food, at first in powdered form and later in tiny pellets, is fed to the tiny fry. As they grow many with imperfections are culled and the rest are grown-on.

All this requires multiple ponds or large tanks which many do not have room nor inclination for. Me included.

There are also a small number of commercial koi suppliers that can be found on-line. Before I discovered the auctions, I bought from some of these but soon stopped. In my experience, their stock is massively over-priced and in some cases, the quality quite abject.

Varieties of koi

Koi is the Japanese word for carp. So if you hear someone saying “koi carp”, they are actually saying “carp carp”.  There are many varieties and sub-varieties of koi, all bearing Japanese names. Youtube has many videos showing all the varieties like this one and this. All can breed with each other which is how different varieties emerged. Sub-varieties include metallic, gin rin (fish of all varieties which have silver scales which reflect sunlight), and doitsu and ‘leatherskin’ fish (those with few or no scales).

Most domestic koi usually grow toabout 38 cm (15 inches) long. Jumbo sized koi can grow up to 92cm (36 inches) but these are seldom seen in Australia. Koi can live for 25-35 years.

A metalic yamabuki ogon, with 2 ochibas below


I’ve had three disasters with my koi in 22 years. The first was when my pond became infected with a virulent outbreak of Aeromonas bacteria which causes nasty skin ulcers, often fatal. The first death occurred while I was away and the person staying in the house missed seeing the floating dead fish which putrefied and infected others. When I returned about half my fish died within days, with others being saved by having an experienced koi keeper come over, catch and inject the sick fish with an antibiotic.

The second occurred when my pump died sometime between 6pm and 8am when I next looked at it. This caused oxygen levels to fall badly in the pond and I woke to find 12 fish, including many of my best, dead in the water.

The third incident occurred a few months ago when a tap topping up the pond was left on for several hours, causing lots of chlorinated water to enter the pond. Eight fish – again mostly my best – were floating dead. Chlorine is fatal to koi and significant tap water top-ups need to be accompanied by the addition of sodium thiosulphate salts or liquid, again purchasable inexpensively at the auctions.

A common problem with keeping koi is overcrowding. There is no strict formula for how many fish you can safely keep in a given body of water, because the different size of fish, the rate of filtration and the quality of your water will all be relevant.  But always consider whether you already have too many fish before you buy more.

Join a koi club

If you are thinking of starting to keep koi, a very smart thing to do is to join one or both of the two koi clubs in NSW. There is a wealth of experience among koi keepers who range from very serious keepers with massive ponds and filtration systems, to people like me with modest sized ponds, and about 15 fish.

I have learned an awful lot, had to filter and research what to do when given conflicting information, met some great friends and immersed myself in a sub-culture and hobby that has given me thousands of hours of pleasure.

Sitting beside our pond on a warm summer’s evening with a gin and tonic, watching the fish glide under the wooden bridge, through the waterfall and around potted water plants is to have a world of serenity at your backdoor. Koi require maintenance and careful watching. I have favourites, but when they have died or been sold after getting too big for the pond, you don’t miss them like you would a dog in your life. They enhance a garden like nothing I’ve ever experienced before.  Highly, highly recommended.

Selected photos

Gin rin ochibas

Simon  Chapman is patron of the Australian Koi Association.