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What is Bacteria?

A single celled organism which may or may not cause disease in an organism.

There are a huge range of species of bacteria, most are still unknown to science and we are still finding out what benefits or dangers they pose to us.

While science may split bacteria into two piles called gram-negative or gram-positive. In the aquarium hobby we often group them into just bad or good bacteria.

Good Bacteria

Nitrosomonas Species: These are the ones that convert Ammonia (released by rotting fish/plant waste) into Nitrite.

Nitrobacter sp. and Nitrospira Species: They convert the nitrite (produced from the breaking down of Ammonia by Nitrosomonas bacteria) into nitrate. Both of these are usually present in the filter.

  • Though Dr. Tim Hovanec claims that it is Nitrosococcus sp. and not Nitrosomonas sp. that converts ammonia into nitrite and Nitrospira sp. and not Nitrobacter that converts nitrite into nitrate. See PDF Paper.

Nitrosococcus and Nitrococcus are the main nitrifying bacteria used in salt water aquariums.

Denitrifying Bacteria: This is the term used for a range of anaerobic bacteria that feed off nitrate and consume the oxygen within and release nitrogen gas. These work in conditions with little to no free oxygen in the water so they consume nitrates.

Waste control bacteria: These are species of bacteria which break down dead organic material like fish waste and dead plant material. (see method - Competitive Exclusion). One such species used in aquariums is Bacillus subtilis found in soil. Believed to also reduce substrate cleaning, parasites and removing odours from tanks. (See Walstad method).

Commercial Bacteria

Bad Bacteria

  • Flexibacter columnaris, recently named Flavobacterium columnare. This common bacteria gives the appearance of white fungus on fish but is actually bacteria. Also called Columnaris, Cotton-Wool, Cotton-Mouth, Flexibacter, Mouth Fungus.
  • Anaerobic Bacteria - This type of bacteria lives in the deeper parts of the substrate and consumes nitrates. However it produces the harmful Hydrogen sulphide gas. Looks like black muck when you stir up the tank substrate.
  • Aeromonas - a nasty gram-negative bacteria that often kills.
  • Corynebacterium
  • Streptococci (Streptococcus sp.)
  • Lactococcus garvieae