Garden ponds are becoming increasingly popular. They enhance the layout of a garden and provide an ideal environment for the wide variety of animals and plants whose natural habitat is in or around open water. Owners of gardens with ponds possess an aesthetically pleasing landscape feature which can also serve as an ecological niche for a large number of animals and plants, including exotic creatures such as goldfish and koi carp.
Garden ponds come in all possible shapes and sizes. The smaller ones are often prefabricated constructions made of glass-fibre-reinforced plastic; larger ones may be may be natural ponds sealed with clay, or they may have been created with the aid of an artificial pond liner. As a rule, some part of the pond will be more than 80 cm deep so that the water does not freeze solid.
In natural, healthy ponds a stable biological equilibrium is maintained. Various plants, fish and micro-organisms make up the so-called food network (see page 11) and thus depend on each other for their existence. If external forces interfere with individual members of this community, then all the other organisms in the ecosystem will also be affected. Within certain limits, a natural ecosystem will be able to cope with disruptive factors. However, the biological balance in artificial ecological systems such as garden ponds with ornamental fish can be permanently impaired by even the slightest disruption.
Most problems in garden ponds are caused by overstocking with fish and by the way the fish are fed. Fish excrement and superfluous fish food cannot be permanently decomposed unless special measures are taken. Man has disturbed the ecological balance of the ecosystem by introducing artificial nutrients. The resultant surplus of fertilized matter (or eutrophication, to use the scientific term) leads to the growth of grass-green algae which clouds the water - and the spirits of the unhappy pond owner.
At first, this does not adversely affect the organisms living in the pond. During the growth phase, the algae produces oxygen, which is released into the water (see figure 5, page 9). Within a few days or weeks, the algae die and sink to the bottom of the pond. As they sink, and after they have come to rest on the bed of the pond, they are metabolized by micro-organisms (bacteria and fungi). These organisms absorb only a very small proportion of the nutrients into their own biomass; the rest is released into the water. The entire degradation process is known as mineralization.
Mineralization, however, uses up the same amount of oxygen as was produced by the algae in the first place. The amount of oxygen in the water is thus rapidly reduced, with the result that the fish and the other organisms in the water suffocate. Once it is in this state, the garden pond can no longer regenerate itself. Intervention is now required.
Fountain pumps or circulating pumps are often used to enrich the water with oxygen and prevent the fish from suffocating. However, although pumping in oxygen in this way will stop the fish from dying, it will not alter the green cloudiness of the pond.
The following chapters explain the individual factors that trigger these processes and provide a detailed description of how the Biotec-Filter operates.
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Oxygen