What is happening when a tank cycles?
  

 

Waste products enter the aquarium in the form of toxic ammonia (NH3).

Fish wastes:

  • The vast majority of ammonia that comes from a fish is that which is excreted across the gills in exchange for sodium (Na+).
  • Fish feces are broken down in the tank into ammonia.
  • Only very tiny amounts of ammonia come from fish urine.

Other wastes:

  • Dead plant material, dead organisms and uneaten food are broken down into ammonia and other by-products as they decay.
Nitrosomonas bacteria convert toxic ammonia into less toxic nitrites (NO2).
  • Oxygen-requiring bacteria, Nitrosomonas, which are naturally occuring in the aquarium, consume ammonia and grow in direct proportion to the amount of ammonia available. The by-product of this process is nitrite.

Nitrospira-like bacteria convert nitrite into less toxic nitrates (NO3).
  • Nitrospiras-like bacteria in the presence of oxygen consume nitrite and grow in direct proportion to the amount of nitrite available. The by-product of this process is nitrate.
Nitrates are controlled through regular water changes.
  • The bacteria responsible for cycling your tank inhabit your filter media, gravel, plants, rocks, wood and other decorations in the tank. They are not free swimming in the water.
  • The tank is cycled when enough bacteria have colonized the tank to process all of the waste produced by its' inhabitants.