Biological water purification zone in a swimming pool.

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Although the biological filter is involved in processing the ammonia excreted by fish, it does not remove nitrates and phosphates coming with food. Nitrates are not as toxic as ammonia and nitrites, but high concentrations of nitrates have a negative effect on fish, inhibiting growth. Some plant species absorb ammonia no less effectively than nitrates, thereby reducing the concentration of the toxin, and, as a result, nitrates.

Since koi ponds have powerful mechanical and biological filtration, the main purification of the pond occurs in the technical section, and the plants play a supporting role. A common method of natural purification of the pond is a flowing bioplateau zone (swamp filter) with suitable plant species and planting floating plants freely or in baskets. The efficiency of water purification is affected by the type of plant, the method and density of planting.

A method of arranging plants in a shallow pool. The roots are restricted slovenia mobile database growing beyond the container and are protected from large fish by large stones.


Some types of plants are more effective at purifying water than others. These are usually fast-growing plants, often with extensive root systems.

Filamentous and unicellular algae act in a similar way, however, with intensive development of algae, the decorativeness of the reservoir suffers or the fish are poorly visible, the parameters change significantly during the day. As autotrophs, algae use inorganic substances such as nitrogen, phosphorus, carbon dioxide and microelements for growth in the presence of sunlight. As a source of nitrogen, they use nitrates or ammonia, some species can absorb amino acids and other nitrogen compounds. Some plants also prefer ammonia to nitrates.

Floating and marsh (semi-submerged) plants are used to purify water.

Floating plants