Are you planning to create a garden pond that respects the harmony of aquatic life? Would you like to create a pond where you and your fish can enjoy serenity, fulfilment and exploration? Plants, insects and animals will come together in a rich, fun ecosystem that you will learn a lot from.

Discover our advice on building your aquatic project.

1. How do I choose the perfect spot for my pond?

Technically, it’s quite easy to build a garden pond if you’ve got the (green) touch, the motivation and the right approach. Choose a location that’s easy to work on, preferably clear and flat. Make sure there are no trees nearby to avoid leaf fall in autumn, which could lead to excess organic matter in your pond and unbalance the water. For life to take hold, it’s best to opt for an east or southeast exposure, as your pond will need plenty of sun. Don’t forget that!

2. What do I need to think about when digging my garden pond?

Once you’ve decided on the ideal location, you will need to dig a hole, always starting at the edges. Let your imagination run wild when it comes to the shape of your pond, but make sure you don’t go for too complex a shape. Keep it simple and effective. There’s a risk that the water will stagnate in certain corners, leading to algae growth and a build-up of silt if the shape is too ‘eccentric’. Water balance is essential if you want your pond to look good in the long term.

The depth of the pond also depends on the aquatic species.
To determine how many centimetres you need to dig, you first need to think about the types of fish you want to introduce into your pond. The minimum depth is 80 cm (guaranteeing a cool summer and a warm winter for your fish). Don’t forget to provide a shady spot in case of a heatwave.

If you want to acquire koi, dig a hole at least 1.20m deep. These ornamental fish can grow significantly (80cm-1m) and need a lot of space to be able to swim freely. You should also keep a close eye on the number of koi you introduce into your pond. If you have too many fish, they won’t be able to grow properly. You run the risk of disease, a direct effect on filtration, which will be slower, and unintentionally injecting more organic waste that could upset the biological balance. Need more info? Read our article about why overpopulating your pond is a bad idea.

How large should my pond be?
With fish, it’s best to follow a few rules:
Adult koi: 5m³ minimum + 1 m³/koi.
Goldfish: 2.5 m³ minimum + 5 goldfish/m³.
Another rule is, beyond the minimum volumes, 50 cm of fish per m³.
Depending on the size of your pond, be sure to give careful thought to the choice of filters and filtration flow, which we will discuss further below.

Plants in the pond?
If you choose to introduce plants, we recommend that you surround your pond to a width of around 50cm and a depth of 30-40cm to avoid undesirable residues in your pond. We therefore recommend installing plants around the pond rather than directly in it, at a reasonable distance so that the mineral balance is not disturbed.

3. Which filters for my pond?

For clear water, we strongly advise you to install a dynamic filtration system to ensure good water circulation. The aim is to get rid of and dissolve the waste remaining on the surface. There are a number of filtration options available, including mechanical or bacterial filtration.

But what are the differences and what is the purpose of these filters?

1. Mechanical filtration

Mechanical filtration is carried out using a grid or certain substrates such as brushes. Its aim is to get rid of organic materials such as leaves, waste, plants, etc. This mechanical filtration (sieve, drum, belt or brush) removes all the coarse particles in suspension.

2. Mixed filtration

Mixed filtration is mechanical and biological, or ‘biomechanical’. It uses substrates that combine filtration capacity with bacterial supports such as Japanese mats. Once the filtering materials have retained the organic materials (nitrites/ammonia), these are broken down by the bacteria present in the biological filter. They are then transformed into nitrates. These transformations are part of the nitrogen process.

3. Bacterial filtration

Biological filtration is possible using substrates that encourage bacteria adhesion. The aim is to keep only the good bacteria, which will promote water balance and fish health, by digesting organic materials.

So you can already see how important it is to measure your water parameters on a regular basis.

The importance of the nitrogen cycle in a garden pond.
As we have already explained, the water in a pond undergoes many changes due to external factors. That’s why you need to be careful to maintain a certain balance in your aquatic ecosystem. Bear in mind that if the water in your pond is not changed frequently, it risks turning green when the temperature rises and the sun shines more brightly.

But what exactly is the nitrogen cycle?

It’s a succession of natural processes that transform nitrogen (N) into organic substances (ammonia, nitrites, nitrates and nitrogen gas). Plant and organic waste (leaves, pollen, fish waste, etc.) decompose and alter the quality of the water, becoming potentially toxic if not closely monitored.

The winning combination is good mixed filtration and a high-performance UV system (purifier and steriliser) to keep your water healthy and clear.

Multi-chamber filters: a simple, economical and flexible solution for your filtration.
For ponds of 2m³ or more, you can opt for this type of filter, which offers a number of advantages and is infinitely flexible. You can add as many as you like, depending on the results you want to achieve. They are robust and suitable for volumes of up to 150m³ (without fish).

4. A pump or gravity mode filtration system?

At what water level should the filter be installed? Do I need a pre-filter? Where should the pump be placed? Does it consume a lot of energy? Here are all the questions to ask yourself before making your choice.

Here are the differences:

Pump mode filtration
The filter is positioned above the pond water level. You will need a mechanical pre-filter to trap all the microscopic waste and to encourage run-off. In this way, the filtration bacteria will be well oxygenated. The pump is placed upstream. In terms of power consumption, it will be higher because of the difference in water level.

Gravity filtration
The filter must be placed at the same level as the pond water. A drum acts as a pre-filter. The pump is installed downstream, and there is a clear economic advantage in terms of electricity consumption, as the filter is at the same level as the pond water.

5. Which substrates to choose?

Context is key to selecting the right substrate.

If there is external pollution such as leaves or petals, use brushes and/or a pre-filter (a sieve).
If the pond has a lot of fish or few plants, use a pre-filter and favour the use of Biocera Home or Matala/Japanese mats. Having fish means inevitably releasing nitrogenous compounds such as ammonia and nitrites, which can be harmful to your fish if there are too many of them, while still being a good fertiliser in small doses. That’s why it’s better to favour bacterial digestion.

UV lamps destroy viruses, bacteria and microalgae in suspension, which will also prevent your water from turning green. If you opt for a powerful UV lamp, you will also be able to combat the development of diseases and parasites on your fish.

Now that the technical side is up and running, it’s time to wake up the decorator in you and let your imagination guide your desires. You will be able to spend some quality time with your family around the pond you’ve been dreaming of.