Aquaponics is the method of growing fish and plants together in a recirculating ecosystem that uses the natural cycles of bacteria to convert fish waste in nutrients for plants.
Image from http://aquaponicgardening.theaquaponicsource.com/
“Cycling” and the nitrogen cycle
CYCLING – To establish a biofilter that enables the nitrogen cycle.
NITROGEN CYCLE – Continuous process in which bacteria convert Ammonia and Nitrites in “food” for plants. One cycle is complete when there is no Ammonia nor Nitrites left in the system. This cycle begins with the introduction of fish in the system, where they release Ammonia (NH3+). Ammonia is toxic to fish unless diluted to a non-toxic level or converted to a less toxic form of nitrogen. Ammonia attracts Nitrosomonas, the first of the two bacteria that will colonize the system and that convert Ammonia into Nitrites (NO2), and the presence of Nitrites attracts an essential bacterium, Nitrospira, which converts Nitrites into Nitrates, which are not toxic to plants and are a good source of food. Whenever Nitrates are detected and the concentration of Ammonia and Nitrites falls to less than 0.5 ppm, we can say the cycle is complete and plants can be introduced into the system.
This is the most conventional way of getting started with an aquaponics system. There are other ones than shorten the “cycling”, e.g., the introduction of synthetic Ammonia or algae and plants in the system (Murray Hallam technique). Unlike a conventional hydroponic system, the pH level should range between 6.8 – 7 because this type of system must take into account the fish, plants and bacteria altogether.