Phosphorus is an important biogenic element that participates in many biological processes, both in plants and animals. In plants (algae), phosphorus is a part of, for example, nucleic acids (DNA and RNA), cell membranes (phospholipids) and a storehouse of cellular energy in the form of ATP (adenosine triphosphate). For algae and cyanobacteria, phosphorus with nitrogen is the limiting element.

Getting nitrogen out of water is much easier than phosphorus. Not only plants, but especially bacteria will help you with nitrogen. Removing phosphorus from a pond is difficult. Plants are the main helpers, bacteria will remove a minimal amount of phosphorus.

Reducing phosphorus in a pond

If there are no aquatic plants (fully submerged) in the pond, but only coastal plants (reed, water hyacinth, frog's-foot trefoil, strawberry plant, etc.), it is necessary to reduce phosphorus and thus limit algae growth. Aquatic plants that are completely submerged consume the most phosphorus.

The content of biologically active phosphorus, i.e. the phosphorus that plants and algae can use, should be below 1 mg/l.

Biologically available phosphorus in the form of total phosphorus pentoxide PO ₄ and its dissociates is very difficult to determine. Phosphorus, together with nitrogen, is the limiting element for algae growth. The optimal molar ratio of nitrogen to phosphorus for algae growth is 16:1. This is the so-called Redfield ratio, which is identical to the ratio in algae and cyanobacteria cells.

Algae and cyanobacteria only use the dissociate of phosphorus pentoxide, i.e. phosphates. If you do not have submerged aquatic plants in your pond, phosphorus can only be removed chemically - by precipitation into an insoluble complex. .

The occurrence of phosphorus in the pond

Phosphorus is a biogenic element that enters the pond in various ways.

• In the spring, garden pond owners are plagued by pollen .
• Phosphorus is contained in fish feed and excrement.
• When plant residues decompose, phosphorus is released from organic material into the water.
• Well water often contains elevated concentrations of phosphorus (fertilizers in the soil).

In a pond, a large amount of phosphorus is concentrated at the bottom in the detritus (mud). From there, it can then be released into the water column and initiate algae growth.

In general, algae and cyanobacteria contain a large amount of accumulated phosphorus, and therefore it is important to continuously remove detritus from the bottom of the pond (with a vacuum cleaner or by applying products). If the pond is well sloped and impurities from the bottom end up in the filtration, it is also necessary to think about a sludge valve.

Reducing available phosphorus can limit the growth of algae in the pond, but it will not prevent the complete disappearance of algae. However, there will be a limitation of growth and a change in the species composition. It is appropriate to apply preparations in the early spring. If the pond is already overgrown with a significant amount of algae, it is more appropriate to choose mechanical removal using a high-quality and safe preparation for eliminating algae in the pond.