Bacteria in pond filters: the secret to effective fish pond keeping
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 the following is needed:
1. 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 in creating 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.
2. 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 filter bacteria and without the oxygen the bacteria die quickly and certainly within 8 hours. Once dead the bacteria colony takes 4 to 6 weeks to build up to a reasonable working level again.
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3. Good water flow rate distributed evenly throughout the filter biomedia bed help the bacteria to do their work. Ensuring good flow through the whole bed is easier said than done. Upflow through the filter bed makes this easier. Biofilters tend to be over-designed to compensate.
For effective total filtration of a fish pond the mechanical aspect of solids removal also have to be good otherwise bacteria holding areas become clogged up. Wash the biomedia frequently using pond water.
Good Pond Filter Design Principles
A pond filter will do a good job if there is a way removing solids effectively and of colonising large surface areas of filter 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 pond 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.
Here's a picture showing a typical box filter (sketch by Peter J May). It's not hard to make a pond filter yourself.
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"The Complete Pond Solver" by Tony Roocroft
2005 Edition. Essential reading for anybody who wants or has a garden pond. Get 12 Excel pond calculators free as well as "Water Lilies and Pond Aquatics" ebook also free
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Best Filter Choice & Prices from America's Top Online Supplier Based in Florida
Biofilters the normal black box type