 Biological filtration has been the subject of more arguments and controversy than nearly any other topic in the field of aquariums. A biological filter can be as simple as the
live rock in a skimmer-equipped Berlin System or the suspended gravel bed and live rock of an all-natural Jaubert Plenum System. A biological filter can also be as complex as a reverse-flow fluidized sand bed/re-aeration system. The most popular biological filters are the under gravel filter and the wet-dry filter. Many years of research have been spent by both scientists and hobbyists alike, all with the same goal - to create or discover the perfect biological filtration system.
There are many biological filtration techniques in use in modern aquariums. Regardless of which method is used, aquarium owners all want to achieve the same end-result, which is to convert toxic ammonia produced by living aquatic animals and the decay of proteins, into less-harmful nitrates through the cultivation of nitrifying bacteria in the aquarium system. Some biological filtration techniques take this
process several steps further, by converting those nitrates into nitrogen gasses through the cultivation of anaerobic bacteria in the aquarium. This process, called "de-nitrification," will be discussed in a future article.
The Basic Nitrogen Cycle in The Aquarium: A simple explanation.
Fish eliminate most of their waste in the form of ammonia. Ammonia is toxic to most animals, so in a brand new aquarium, the first fish introduced must be very hardy species which are known to be able to tolerate ammonia in the water. Eventually, beneficial bacteria will cultivate in the biological
filter, gravel, rocks, and any other surface in the aquarium. These bacteria are aerobic, meaning they need oxygen to survive, the same as us. They are also known as "nitrifiers," as they consume ammonia and ammonia by-products and convert them into less-harmful substances that fish can tolerate. These bacteria will cultivate in far greater populations, in any area where the highest amount of oxygen exists, which is usually in a filter system that is designed to promote their growth by
supplying a continuous source of oxygenated water to the bacteria. This is where the term "biological filtration" comes from.
The Nitrogen Cycle
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The first species of bacteria to appear on the scene in a new aquarium are Nitrosomonas species of bacteria that "feed" on ammonia, and convert it into nitrites. Nitrites are a little less-harmful than ammonia, but are still rather poisonous. Eventually, usually within two to three weeks, Nitrobacter species begin to cultivate. As the Nitrosomonas populations came first, it usually takes the
Nitrobacter species a longer time to cultivate into a full population. Nitrobacters "feed" on nitrites and convert them into far less harmful nitrates. Many fish can tolerate relatively high levels of nitrates, but if nitrate levels get too high, fish will begin to suffer.
In nature, all of the nitrates produced by bacterial nitrification are consumed by plants, algae, other species of bacteria, and other organisms. In an aquarium as in nature, nitrates are used by plants and algae as food, and in some cases, are also converted by anaerobic bacteria into nitrogen gases. A so-called "balanced" aquarium, is one where the ratio of plants or algae to fish is balanced, so
that all of the nitrates produced are converted or consumed, so no nitrates exist in the water. This is very difficult to achieve in practice, as such an aquarium will have very few fish, and that is not satisfying to most aquarium hobbyists. To control the nitrate levels in an aquarium, we do water changes. That is why water changes are so important. They lower nitrate levels before they get too high and become a hazard to fish.
Biological Filtration Types and Techniques Explained
So what is the perfect biological filter? The perfect system would allow an aquarium owner to maintain a beautiful aquarium with plenty of desired livestock, with a minimal amount of work required to maintain the system in peak condition. The Aquarium Professionals Group has conducted plenty of our own research on biological filtration in our aquariums, and have installed various systems over the
years. It is our opinion that the perfect biological filter is one that best meets the needs of the aquarium occupants. Our first priority is the well-being of the fish and invertebrates we maintain. We design aquarium filter systems around the type and quantity of animals our clients desire. Our goal is always the same: Keep the animals entrusted to our care alive and healthy!
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