It is important that before adding plants and fish to your newly aquaponics setup that you start it cycling. No, I don’t mean go and ride your bike, but you need to establish the bridge between the fish and plants by establishing the bacteria.
Bacteria are the magic ingredient that converts unusable fish waste to plant fertiliser. The bacteria create a symbiotic eco-system without the problems that are found in aquaculture and hydroponics.
Cycling is the process that establishes the nitrogen cycle in the system. The nitrogen system is the ongoing process that converts ammonia produced by the fish into nitrates that the plans can consume.
Cycling starts when you add ammonia (NH3) from fish or other sources into the system. Ammonia is toxic and can quickly kill fish unless diluted or converted into another less toxic form of nitrogen. Ammonia is not readily used by plants, and must be converted by bacteria into a plant usable form.
Ammonia attracts a nitrifying bacteria called Nitrosomonas, that converts the ammonia into nitrites, which is even more toxic to fish. The presence of nitrites attract another nitrifying bacteria call Nitrospira, which convert the nitrites into nitrates which are the plant food needed.
It is important to regularly test the water in the aquaponics system to monitor ammonia, nitrite and nitrate, and pH levels, to ensure that they are kept in range.
You can start the cycling process using fish, but this is perhaps the most stressful option, as they can die. It is also possible to start the nitrifying process using liquid ammonia (pure ammonia or pure ammonium hydroxide), or humonia (pee-ponics). To start using these methods, add ammonia until the reading is 2-4ppm, and keep adding that amount daily until nitrite appears at over 0.5ppm. If the ammonia level goes over 6ppm, stop adding the ammonia, until back between 2-4ppm.
I think it is important to add plants to the system before starting cycling, as they can start using any nitrates in the system. My water in the system already had ammonia, nitrites and nitrates as I took it from my dam containing fish, ducks and yabbies.
Seasol, a seaweed based fertiliser available in Australia, is also an excellent way to start the cycling process. After adding the Seasol, and plants, check the ammonia, nitrite, nitrate and pH levels, wait 2 weeks, then fish can be added at a low density. More fish can be added once the system has stabilised and plant growth has started.