Sustainable Koi pond.

Reading Time: 7 minutes

written by Hugo J. Smal

Sustainable Koi pond.A sustainable Koi pond makes sense.

Energy is expensive and will get more costly. The environment is in trouble. We must improve that very quickly. Otherwise, we’re all going to die. I must admit that the Koi hobby does not play a positive role. The fish all make a considerable flight. The pond itself uses a lot of electricity. We can do a little about the first. Let them swim? We can reduce power consumption. On behalf of the Goyang Koi farm, I am starting what will hopefully become a discussion within the hobby. Is a climate-neutral Koi pond possible?

Koi law.

Until now, the law within our hobby was: koi and pond plants do not go together! Koi in a natural garden environment is not possible. Carps are fond of plants. They dig them out and suck off the soft tissues. A natural Koi pond becomes a disaster with dead plants and sick fish. However, it will probably have to be different. The energy costs and the major milieu problem force us to reconsider this law.
Koi enthusiasts worldwide adhere to the law: no aquatic plants in the Koi pond. Except for several ‘dissidents’, who let one or two swim in their pond. They do want to enjoy the beautiful colours of the ornamental carp with a basic positive attitude but also want to experience the seasons. Aquatic plants, frogs, salamanders and other aquatic inhabitants also fulfil a function.

Nature is banned or never allowed in the ponds of true koi fanatics. They maintain water quality using large filters, UV radiators, ozone generators, bottom drains and more such technical aids. The fish are the central focus point. You often see that the pond looks great. But that the garden is a stepchild. That is a pity. After all, the garden and pond can have a very positive effect on the environment.

Sustainable Koi pond.The natural way.

The most important cycle in the pond is that of the feed. Fish get what they need from this and relieve themselves of the rest. The waste enters the pond as ammonia and nitrite. Bacteria convert these harmful substances into nitrate. This is plant food. It’s a simple cycle. I hope every water gardener can dream it.

We Koi freaks intervene in this cycle in two ways:
the conversion by bacteria of the harmful substances they concentrate in the filter
Plants do not remove from the water by plants (because there are none) but through water changes.

If they do not regularly change part of the pond water, the pond will quickly turn green. We find that annoying because then we don’t see our beautiful carps. This food cycle intensifies in the Koi pond. (usually too much fish and food) and causes pressure on the water quality. The water feature is always in a precarious balance.

Plants make the sustainable Koi pond.

When we use marsh plants to make healthy water we also let the bacteria do their work in the pond. This has many positive consequences. I name two:

– the construction of the koi pond is a lot more energy-efficient because all those peripherals are needed less.
– the pond becomes self-regulated.

It will be obvious. Koi freaks prefer all that equipment to the natural way for a reason. They want to fish as much and as large as possible. That requires a lot of food. If you choose a natural way of keeping Koi, you must reduce the number of carps.
In addition, many people experiment with keeping the beauties in natural ponds. Much of them vailed. Still, I think it should be possible, as long as you stick to the restrictions.


Iris laevigata
Iris laevigata by
Equisetum japonicum

A sustainable dream pond.

We find all kinds of minerals in a natural pond. This is good for koi. They contribute to the quality of the fish. In addition, all kinds of animals swarm in the water. They form a good addition to the daily menu. A big advantage is that the fish will get bored less quickly in a natural water feature than in a bare tank. Koi are curious animals. They like to investigate everything. It works stress-resistant if they are allowed to do so. These are all reasons to pick up the experiment again. Let’s call it a dream pond on paper for now.

The requirements and preconditions for the self-sustaining pond at a glance:

1) We assume that the water in the koi pond is controlled in the most natural way possible.
2) As few devices as possible are used to support the water quality.
3) Plants and fish should be separated so that the fish cannot destroy the greenery.
4) The number of plants must be such that the fish can be fed enough. They must grow well and not lose quality.
5) The pond should be self-regulated with as little maintenance and water changes as possible.

Sustainable Koi pond.The design.

I choose a Sustainable pond. with a natural appearance. This means no walls steeply downwards, but sloping with a large, deep part more towards the middle. However, there must be a raised edge or shielding to prevent the fish from swimming on the bank during heavy sex. I built a gutter around the pond, in which aquatic plants will provide a natural transition between water and land. This will also serve as a swamp filter. The soil from the pond is collected at a location where a higher plant pond will be built. This connects to the gutter around the fish pond via a waterfall.

The materials.

For sealing my dream pond, a bentonite pond liner is a good choice. This is a natural product and therefore the ideal bottom for the Sustainable pond. This mat consists of a natural type of clay (bentonite), wrapped in geotextile on both sides.
Bentonite originated about 30 million years ago and is the clay with the highest swelling capacity. As a result, the material remains waterproof even around posts and penetrations. It is also self-healing: small holes close automatically.
Because this material must have counter pressure or else rise it will continue to swell and dissolve. A substantial layer of the substrate must be placed on the bottom. It forms a good attachment site for the bacteria that convert nitrite into nitrate. That is why I would also apply the substrate in the plant pond and gutter.
Furthermore, I only place a professional pond pump (on solar energy) to control the waterfall and a sieve that separates the floating dirt from the water. Dirt then ends up on dry land and does not have to be processed by the bacteria.

Sustainable Koi pond.Plants eat nitrate from the sustainable Koi pond.

The water cycle is now easy to describe: nitrite converts into nitrate in the substrate at the bottom of the fish pond. It happens wherever the substrate is located.
From the bottom of the fish pond, the water is pumped up to a sieve, located behind the plant pond. Solid waste separates from the water here. In the normal koi pond, we use brushes, a settling tank or a vortex. The water then flows into the plant pond, where the plants absorb nitrate and store it in their leaves.
The water then pours through the waterfall (extra oxygen addition) into the plant gutter, where the plants and the substrate have the same beneficial effect. Then the water flows back into the fish pond.

Nitrate Eaters.

The plants that we use to combat nitrate are the so-called pioneer plants, which appear first on new land in free nature. You will encounter them in abundance in new polders.
I mention four species: Typha angustifolia and Typha latifolia (the lesser and the greater bulrush) T. Angustifolia grows up to 150 cm high. T. latifolia adds another 50 cm. We can buy Carex or sedge in 5 varieties. They grow to an average height of about 50 cm, while the flower stems shoot up to 150 cm. Phragmites australis (reed) is a plant to watch out for, simply because it grows quite large and grows vigorously. The cultivar ‘Variegata’ is more suitable for the garden pond. Scirpus is available in four varieties. The best looking for my application is probably Scirpus lacustris ssp. tabernaemontani ‘Zebrinus’, because it is strongly reminiscent of the Japanese hollow pipe.

Cover: A Koi life.Boost your Koi dedication.

Our writer Hugo J. Smal published his book: A Koi life. It is about: the beautiful Koi, lovely Korea and his life dedicated to that. Much information about the Koi. Reading it gives your Koi dedication a boost.  You also get an introduction to Korea and the Koi they breed there: K-Koi. All this for just € 3,95.  Buy now!

Plants in the self-sustaining pond.

All these plants have in common that they can be harvested in the autumn. Nutrients will disappear from the pond. You can also prune them back to about forty cm during the season. I plant them in the plant pond and at the back of the fish pond because otherwise, they obscure the view of the fish.
Furthermore, I would vary widely with water lilies, irises and many other marsh plants. Put oxygenated plants in the plant pond.

When we construct a sustainable pond. and decorate it in this way, the decoration of the garden will follow naturally. A natural and perhaps even romantic environment has already been created with the used plants. I think of vistas with roses, paths of old stones and what is most important to me: a terrace adjacent to the pond, enclosed by fragrant plants in colourful borders.

I am aware that there are a lot of people worldwide who manage their fish ponds in this way. There are even those who provide themselves with a delicious meal: aquaponics! I’d love to hear about your experiences. Leave a message below.