Filtration is often required in formal ponds and smaller natural ponds. Larger natural ponds tend to be less prone to problems with algae and the use of bacterial products (Live Liquid Micro-Organisms) are often the preferred method in larger ponds and lakes because of the cost of mechanical filtration.
Filtration can be carried out in several ways. Our preferred method is the use of gravel bed filtration, similar to that used in some swimming ponds. This can be done in two ways. One is to construct a filtration bed within the pond using a low retaining wall to contain the gravel. Alternatively, a small filtration pool can be built next to the main pond and water can flow into it. The water is then pumped back up into the main pond. Done this way, the filtration pool also acts as a skimmer as leaves and floating debris drift into it via the movement created by the water pump. Either method can be made to look attractive by planting aquatic plants in the gravel, with the plant's roots also helping with filtration by absorbing nutrients from the water. Dark grey gravel can be used to help make the gravel beds less obtrusive.
We also use a live bacterial anti-algae product which consumes the nitrates and phosphates that are in our water, thus depriving the algae of its food source and greatly reducing the likelihood of green water and blanket weed. In the last ten years, this has become a popular and successful method of algae control in both large and small bodies of water.
If a minimal look is required in the pond design an external balance tank can be installed at ground level. This can be some distance from the pool, with the water in it at the same level as the main pool. The balance tank can contain the power supply, water pumps and a chlorine/bromine dosing unit which will destroy algae. A UV filter can also be installed in the balance tank as well as a water top-up system and overflow. A chlorine dosing unit cannot be used if fish or plants are desired.
Finally, there is the good old black box filtration system which is filled with filtration media on which live the beneficial bacteria that help control algae. Water is pumped up from the pond and passes through the filtration media and returns via a pipe back to the pond. They are bulky so you need somewhere to hide them from view.
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