Cycling Aquaponics Systems
Starting up your aquaponics system involves getting beneficial bacteria established in the grow bed. This process is known as cycling and is vital to the success of your system. This article covers cycling aquaponics systems in detail.
Toxic substances are produced from fish waste and respiration, and these have to be broken down into a form that can be absorbed and used by the plants. This is carried out by beneficial bacteria that colonise the grow beds.
The process by which fish waste is broken down and used by the plants is known as the nitrogen cycle, hence the term “cycling”. Ammonia from fish waste and respiration is converted into nitrite by bacteria known as nitrosomonas. The nitrites are then converted into nitrate by bacteria known as nitrobacters. The nitrate is then absorbed by the plants. Essentially, bacteria converts fish waste into food for the plants, at the same time keeping the fish safe.
However, in a new system this beneficial bacteria has to build up and establish itself. In order to do this ammonia is added to the system, providing a food source for the nitrosomona bacteria. During cycling, aquaponics system grow beds are colonised by bacteria. These bacteria are built up to such a level that they can cope with the levels of ammonia produced by the fish.
Click Here for the definitive guide to Aquaponics
As the nitrosomona bacteria converts ammonia to nitrite, it provides a food source for the nitrobacter bacteria. Again, during the cycling process, these bacteria are built up to such a level that they can cope with the levels of nitrite produced by the nitrosoma bacteria.
When the nitrobacter bacteria converts nitrite to nitrate, it provides a food source for the plants.
There are two methods of cycling aquaponics systems, with or without fish. If fish are used, they are the source of ammonia. With fishless cycling you provide the ammonia source, thereby taking the fish out of the equation.
Fishless Cycling should be used for a number of reasons. First and foremost is the well-being of the fish. Cycling aquaponics systems with fish is stressful for the fish at best. High levels of ammonia causes burns, especially to the delicate gill structures. Even though the fish may survive, their future health will be compromised and their lifespan will be shortened.
Also, fishless cycling is quicker and involves less work. Because you can have a much higher concentration of ammonia than you could with fish, the process is speeded up. Fishless cycling takes from 10 days to 3 weeks, as opposed to 4-6 weeks if you use fish. Cycling aquaponics systems with fish also means lots of water changes. Once a system has cycled you can fully stock the fish tank, whereas if you use fish you have to stock it gradually. Also, with fishless cycling you can control the concentration of ammonia so it is at an optimum level.
Sources of Ammonia
There are two recommended sources of ammonia – liquid ammonia and ammonium chloride.
Ammonium chloride is pure ammonia in crystalline form. You can get this from aquarium shops, sold specifically for cycling. If you buy it from another source, make sure it is food grade to be on the safe side.
Liquid ammonia is sold as a cleaning product and is safe as long as you use “pure” ammonia. Pure ammonia is actually ammonia diluted with water, usually between 5 and 10%. If it has anything else added then avoid it. If you shake the bottle and it foams it will have additional ingredients, such as surfactants, perfumes etc. You can get this from a hardware store, or failing that, try online.
In addition to a source of ammonia you will need to monitor the levels of ammonia, nitrite and nitrate. You can do this with simple, inexpensive test kits sold for aquariums eg. the Hagen Nutrafin range of test kits.
Fishless Cycling Step By Step
- Gradually add ammonia to the tank until you get a level of around 2 ppm
- Test daily until there is no trace of ammonia (this may take several days)
- Add more ammonia to bring it back up to around 2ppm
- Repeat this process until you get no trace of ammonia 8-12 hours after adding it to the tank
- Test for nitrite
- If there is no trace of nitrite, go to the next step. If not, repeat the previous step 3-4 times then test again for nitrite
- Do a very large water change (about 90%), making sure the water you add is around the same temperature as the water in the tank
- Add your fish
Speeding Up The Cycling Process
When cycling aquaponics systems, the process can be speeded up by adding bacteria to the system, rather than waiting for it to show up on it’s own. Heating the water to the optimum temperature will speed things up further.
Bacteria can be obtained from the following sources:
- Media from an existing aquaponics system
- Filter media from an established, disease-free aquarium or pond
- Squeezings from a filter sponge, from an established, disease-free aquarium or pond
- Gravel from an established, disease-free aquarium
- Commercial bacteria product eg. Cycle – the jury is still out on the effectiveness of these products
The best temperature range for cycling aquaponics systems is between 86-95°F (30-35°C). This is the optimal range for the nitrifying bacteria. You can use a suitably rated aquarium heater, or multiple heaters, to raise the temperature during cycling. You will need to monitor the temperature, and the easiest way is to use a floating pond thermometer. Once cycling is complete allow the temperature to drop to the right level, then do a water change as mentioned previously.
Click Here for the definitive guide to Aquaponics