Bacteria, fungi, water molds, wood, algae, mulm, protozoa, plants and, indirectly, fish can absorb nitrates, nitrites and ammonia from the water and produce proteins. This can reduce the nitrogen compounds by something called “assimilatory denitrification”. It is common and well-documented.
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8.9.2. A Feasible Reactor for doing Anoxic Aquarium Filtration
A Feasible Reactor for doing Anoxic Aquarium Filtration is possible but not worth the effort.
8.9.1. Biocenosis Reactor
Testing of Biocenosis reactors shows they don’t work!
8.9. Anaerobic or Anoxic Reactors as an Aquarium Filter
Anaerobic or Anoxic Reactors as an Aquarium Filter cannot reduce nitrates to nitrogen gas, this article shows why!
8.8. Filter and Media Design for Aquariums
Filter and Media Design for Aquariums: how to calculate the size and media for your aquarium filter.
8.7.8. Small DIY Aquarium Filters
Small DIY Aquarium Filters: this article shows some 16 different alternatives.
8.7.7. Bottom of the Tank Matten
Bottom of the Tank Matten filter consists of a combination of under-gravel plates with a substrate of charcoal colored foam instead of gravel.
8.7.6. Small Filters for the Aquarium
Small Filters for the Aquarium only do decent filtration in small aquariums with small numbers of small fish!
8.7.5. Do it yourself Aquarium Bottle Filters.
Do it yourself Aquarium Bottle Filters are very cheap to build. They are also very poor filters.
8.7.4. Aquarium Diatomaceous Earth Filters
Diatomaceous Earth Filters could be used to filter out ich, parasites and bacteria. However the filter plugs very easily and is no longer produced.