The Basin Filter
The installation of an organic or mechanical filtering system is necessary if you wish to have crystal-clear water in your garden basin all year round. Choose the system bearing in mind the size of the basin and its use - a water source, a fish pond, etc..
A garden basin isn't simply for ornamental use - it also plays a role in the biodiversity of your garden. It must therefore be equipped with an adapted filter if you want to have crystal-clear water all year round.
There are two main criteria to be taken into account when choosing the system of filtration : the size and the use of the basin. These criteria are often linked. Basins used for accomodating large fish like the Koî or Japanese carp must be fairly big and must therefore be equipped with a corresponding filter.
Ornamental basins which only accomodate plants are usually smaller, as are those used for goldfish, etc.. Unless you want to create a complicated lagoon-like network, it is best to buy a filter from an ordinary gardening retailer.
The two main types of filtering systems
Although many types of filtering systems exist (surface filters, cascade filters, pressurized filters with ot without an emptying outlet, multi-chamber filters, etc.), there are two main varieties : organic and mechanical systems.
Organic filters work on the principle of the presence of friendly bacteria which eliminate waste like fish excrement, decomposed vegetation or other organic matter naturally from the basin. This bacteria is concentrated on different elements of the filter (organic shots, lava stones, nets, etc.). The most commonly used ones are barrel filters.
Mechanical filters work differently. They are fitted with a pump which passes the water through a sheet of foam and a mesh. These help trap the floating particles to be eliminated and must be cleaned regularly. The best filters on the market are those which use both the mechanical and the organic process. These are multi-chamber models which have both a mechanical part and an organic part.
The most sophisticated filters also have a water sterilization system incorporated. These systems uss ultraviolet light which limits the spread of algae in the basin. These filters can be pressurized or not, depending on the size of the basin and on whether there are fish present or not.