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How to Select a Bio-filter Based Upon Pond Water Volume

To specify an appropriate biofilter it is important to know the volume of water in a pond to say about 80% accuracy. A filter is specified in terms of what capacity it can handle when the pond is stocked normally whatever that is. Remember as fish grow you can always add more biomedia to cope with the higher feeding rates and greater levels of pollutants.

Typically therefore a filter will claim to handle or purify up to 5,000 litres of pond water. The claim will be based upon qualifications such as fish stock density, amount of food fed and so on. If you can afford it always go slightly bigger to get better performance.

Installing a biofilter without a UVC is no guarantee of clear water (although it is possible you will be told it is do not believe it) because clear water is dependent not just upon the filter design. It is dependant upon other system components like churning because too large a water flow is passing through the pond. Another reason for cloudy water is the presence of algae, which are far too small to be taken out by all the pond filters on the market that I am aware of. However a well-designed filter will go a long way to giving you clear water (where the lack of clarity is resulting from solid particles and not algae).

If you intend to keep fish you must have a biofilter unless you want impure water and dying fish.

Do reconsider your intention to build a pond if you are not prepared to spend money on a biofilter. You will be wasting money if you go ahead without a biofilter and I promise you will do it sooner or later or you will turn the pond into a sand pit.

Biofiltration - understand it well and always consider that generally speaking a garden pond has too many fish for its own good. In a garden pond fish consume food and excrete waste products. The waste products build up in the water unless they are continuously removed and that's why you need a biofilter for every fish pond. In simple terms the pond water is also the toilet water.


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