The filter trench as a natural filter chamber
First of all: the pond filter option of the filter trench is only suitable for large plots of land. Because depending on the pond's function, the ditch must take up a large proportion of the volume of the pond itself. The ditch must be particularly large in ponds that are particularly polluted by a lot of water movement and the ingress of foreign bodies. Above all, this includes:
- Ponds with fish stocks
- Swimming ponds
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With these types of ponds, the Filter trench occupy at least 20% of the pond size. In the case of fish ponds with a high population density, it is even advisable to design the filter trench as large as the pond itself.
How the filter trench works
A filter trench is created near the pond and connected to it via an underground hose. Its task is to continuously flush the pond water in the sense of a filter pump system and to give it back to the pond in a clean state. That means: A circulation pump at the end of the trench is usually necessary anyway. It conveys the water from the ditch inlet to the exit and back into the pond. The difference to the complete filter pump system: Plants take over the water purification instead of the filter inserts.
The cleansing power of plants
A filter trench must therefore be equipped with plant species that have a particularly high nutrient turnover. In addition to suspended solids, they should also break down amino acids, convert nitrate to nitrogen and release oxygen. Plants that are good at this are, for example:
- Sweet flag
- Cattail
- Frog bite
- Crab claw
- Water star
If you use such clarifying plants in the filter trench, you can plant your pond purely according to ornamental aspects.
In order to make the clearing process optimally from coarse to fine, you should place reed beds and floating leaf plants at the beginning of the trench and more finely branched underwater plants further back.
Shape and structure of the trench
The trench should ideally run straight so that the flow of water can proceed as undisturbed as possible. Incidentally, this is also easier for building and laying out with foil. In the initial area, you should fill the trench with pebbles that are as free of lime as possible. So that the trench disturbs as little as possible and does not take up as much usable space in the garden, it makes sense to create it on a long side of the edge.