Bacteria ... the secret to effective pond filtration
The more bacteria you have in any pond filter the better your pond water quality will be. These bacteria transform toxic chemicals in the pond water secreted by the fish into plant fertilizer suitable for pond plants. For any biofilter to work well you need reasonably good mechanical filtration (solids removal) before the water enters the biological chamber in the biofilter. The better the removal of solids the better the biofilter will work and a large colony of specific bacteria that literally eat the waste products from the fish. The bacteria convert this waste to nitrate chemicals, which act as a kind of fertiliser for plants growing in the pond. The larger the colony of bacteria the more quickly they can destroy waste build-up.
The more surface area that can be incorporated into a filter the better.
An attempt (albeit a basic attempt) to achieve this is by placing hollow tubes of rough plastic inside the filter box. Other attempts include the use of orange bags, lava rock, tubes, and even hair curlers. Certainly all of these methods create holding areas for the bacteria but they are all inefficient and therefore large sized boxes are required to create sufficient area for the bacteria colonies to grow on. The generic term for all these substrates used for holding bacteria is BIOMEDIA - a medium to hold bacteria.
Foam sheets by virtue of the many small holes in them also provide surface on which bacteria can grow as well as acting as a mechanical filter to remove solids.
By far the best means of getting large surface area into a small black box biofilter at low cost is to use porous ceramic materials like Alfagrog. This is a product made in the UK specifically for fishpond water purification. It has a massive surface area of between 40 and 100 sq. metres per litre depending upon the particle size compared to 0.2 square metres per litre for plastic tubes.
Without getting too technical this means that 1 litre of Alfagrog can hold the same amount of bacteria as 200 litres of plastic tubes. In other words a box using plastic tubes needs to be 200 times bigger in volume than one containing Alfagrog to get the same biological performance.
You also need
A continuous supply of oxygen to enable the bacteria in the filter to live. This is why a pump must work 24 hours per day since the water is the source of oxygen for the bacteria and without the oxygen the bacteria die quickly and certainly within 8 hours. Once dead the colony takes 4 to 6 weeks to build up to a reasonable working level again.
Good water flow rate throughout the filter biomedia. And not just through portions of the bed easier said than done by the way so biofilters tend to be over-designed to compensate.
For effective total filtration of a pond the mechanical aspect of solids removal also have to be good.
Good Pond Filter Design Principles
A filter will do a good job if there is a way removing solids effectively and of colonising large surface areas of bacteria that are able to intimately contact the water containing the waste products pumped through the system and if there is continuous flow of oxygenated water through the biofilter we tend to use the word filter as a short version of biofilter. The more surface area that can be incorporated into a filter the better. An attempt (albeit a basic attempt) to achieve this is by placing hollow tubes of rough plastic inside the filter box. Other attempts include the use of orange bags, lava rock, tubes, and even hair curlers.
Heres a picture showing a typical box filter (sketch by
Peter J May, Pond
Detective)
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Alfagrog is called Supra in USA Alfagrog is called Supra in USA and can be bought here ... it is best all purpose media for small to medium ponds . Alfagrog looks a bit like cinders, it is lightweight, comes in different sizes and you can literally blow through it because it is so porous.
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