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SESK: Stuff Everyone Should Know · sesk.info/fish-ammonia-to-nitrite

What do beneficial bacteria turn ammonia into first?

Nitrite, the second step in the aquarium nitrogen cycle.

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  1. Nitrite ✔
  2. Nitrate
  3. Oxygen

Why: Nitrifying bacteria oxidize ammonia to nitrite. Another group later turns nitrite into nitrate.

Huh, didn't know that: In a tank, the bacteria need a filter as a place to live and grow.

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References

Answer: Nitrite. Nitrifying bacteria oxidize ammonia to nitrite. Another group later turns nitrite into nitrate.

  1. UF/IFAS Extension FA031: Ammonia in Aquatic Systems edis.ifas.ufl.edu/publication/FA031
    Ammonia-oxidizing bacteria convert ammonia to nitrite, and nitrite-oxidizing bacteria convert nitrite to nitrate.
    Checked 2026-10-11.
  2. UF/IFAS Extension FA031: Ammonia in Aquatic Systems edis.ifas.ufl.edu/publication/FA031
    In tanks or aquaria, a biological filter ("biofilter"), must be provided as a place where the bacteria can colonize and flourish.
    Checked 2026-10-11.

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