A Beginner's Guide to Keeping Koi

Few cold water fish can compete with Koi, whether that’s in terms of their variety of patterns and colours, their long history and cultural traditions, or just their sheer physical presence. Koi appeal for all sorts of reasons; for some people, the opportunity to own some of these remarkable – and highly valued – fish is the reason they built a pond in the first place, while for others, the interest develops later, sometimes years after they first became involved with ponds and water gardens. Whenever the bug bites, however, it is important to recognize from the outset that although the basics of their management remain much the same as any other type of pond, successfully keeping Koi does require a few unique demands to be met.

Planning the Pond

These are potentially very large fish, often growing to between two and three feet (60 – 90 cm) in length and sometimes up to four feet (1.2 metres) or more, which obviously means they call for a sizeable pond to house them, particularly if you plan to keep several specimens. As a good general guide, the pond should be no smaller than eight feet by six feet (2.4 metres x 1.8 metres) at the surface, and four feet (1.2 metres) deep.

Ideally you should aim to build as large a pond as you can possibly accommodate, since the greater the volume of water it can hold, the more stable the conditions will be, and the less susceptible it will be to changes in temperature if the weather suddenly turns unexpectedly hot or cold. All of that adds up to helping reduce the stress on your fish and should hopefully see them stay in the best of health.


Good filtration is another important aspect of keeping the water in top condition, since these large fish produce a significant amount of nitrogenous waste, particularly during the warm summer months, when they are feeding well and are at their most active. There was a time when the Koi enthusiast had almost no choice except to build his or her own filter, but these days there are a number of proprietary brands widely available that have been designed specifically to meet the particular needs of the Koi ponds. Frankly, unless there are very good reasons – and there really aren’t that many – to build your own, the new Koi keeper is always best advised to pick a suitably sized commercial version, and take all of the worry out of this aspect of things. They are rated in terms of the volume of water they will comfortably treat, and either come with suitable pumps to make a complete packaged system, or with clear recommendations as to the flow rate of pump needed to drive them properly – which again obviously makes things very simple for the novice enthusiast.

Plants for the Koi Pond

Unfortunately, it is very difficult – bordering on the impossible – for Koi to co-exist with plants, except when the fish are very small, as their natural inquisitiveness, coupled with their foraging behaviour usually results in your carefully chosen water plants being uprooted, eaten or both! Sadly, as a general rule, this means there isn’t really a place for plants in this kind of pond.

If you are really determined to try, however, water lilies can sometimes prove successful, particularly if you pick some of the more robust varieties, and grow them in planting baskets that are too large for the fish to overturn. Alternatively, marginals can be worth a try if your pond design allows for a marginal shelf, but only if it’s too shallow for the Koi, or otherwise your planting scheme is unlikely to remain unmolested for long.

Stocking Density

When it finally comes time to select your fish, it is very important not to get carried away and over-stock your pond – no matter how tempting it may be to add just that extra one or two. A good rule of thumb for the novice Koi keeper is to aim at a stocking level of around 50 inches (125 cm) of fish per 1000 gallons of water – which means that our ‘minimum’ 8ft x 6ft x 4ft pond, which holds approximately 1150 gallons, could safely support Koi up to a total length of about 58 inches (145 cm).

Koi Varieties

Although we tend to associate Koi with Japan, where they have been popular for centuries, they actually originated in China, perhaps as long as 2,000 years ago, when the ancient Chinese developed ways to breed colourful versions of the Common Carp (Cyprinus carpio).

The modern fish we call ‘Koi’ (from the Japanese word for ‘carp’) and are known in their homeland as ‘nishikigoi’ (brocaded carp), owe their existence to fish breeders in the Nigata region of Nineteenth Century Japan who began the selective breeding programmes that produced today’s colourful varieties. The first types were probably the red and white fish, known today as Kohaku, with the red/white/black Sanke and Showa forms being next to be produced.

From these beginnings, a whole range of other distinctive types have emerged over the years, distinguished by their colouration, body patterns and scales, including the likes of:

  • Ai Goromo – a white fish, with a pattern of red scales, each being edged in deep blue.
  • Aka Bekko – a red fish with black patterning
  • Asagi – an old and very popular variety, with a white head and a body pattern of pale blue scales.
  • Ogon – a metallic looking single coloured Koi, gold and platinum being particularly popular
  • Shusui – a striking fish having only a few large ‘mirror’ scales on an otherwise scale-less body.

There are, of course, many more, and new varieties and types are still being developed – making deciding which are your own personal favourites one of the most interesting and rewarding aspects of keeping these fascinating fish.

Do be aware, however, it can quickly become an addictive and all-absorbing hobby. Many is the enthusiast who started off with one pond, and then built another, bigger one – and then another. You have been warned!