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Building and preparing the unit

Detailed step-by-step building instructions are provided in Appendix 8. Once the unit is complete, it is time to prepare the system for routine function. Although aquaponic unit management does not require excessive time and effort, it is important to remember that a well-functioning system requires a minimum of 10-20 minutes of maintenance every day. Before stocking a new system with fish and planting the vegetables, it is crucial to ensure that all of the equipment is working properly. The most important aspects to check are the water pump, the air pump and water heaters (where applicable). It is essential to check that the NFT pipes and media beds are steady and balanced horizontally. Start running water in the system and make sure that there are no leaks or loose plumbing connections. If there are, tighten or fix them immediately. Section 9.3 provides further methods to secure the water levels and prevent catastrophic loss-of-water events. Once built, cycle the water for at least two days in order to let any chlorine dissipate. This process can be accelerated using heavy aeration. This is not necessary where the source water contains no chlorine, such as rainwater or filtered water.

Media bed unit preparation

The growing medium (volcanic gravel, expanded clay) should be well washed. Fill the beds with the medium and let the water run through it; the water should be clear. Remove any sedimentation (if present) by flushing out the beds with water. If using an electric timer to flood and drain the beds, it is important to synchronize the time it takes to fill the growing beds and the flow rate of the water entering the bed. If using a bell siphon, the water flow rate should be adjusted to ensure the auto siphon function. The water flow rate must be enough to activate the siphon, but not so strong that it prevents the suction from stopping.

NFT and DWC unit preparation

Make sure that the water flowing into each grow pipe or canal is flowing at the right rate (1-2 litres/min for NFT; 1-4 hours retention time for DWC). Higher flow rates have a negative impact on the plant roots, while lower flow rates do not supply adequate nutrients or oxygen.

System cycling and establishing the biofilter

Once the unit has passed the initial component checks and has been running for 2-3 days with no problems, it is time to cycle the unit. As discussed in Chapter 5, system cycling is the term that describes the initial process of building a bacterial colony in a new aquaponic unit. Normally, this is a 3-6 week process that involves introducing an ammonia source in the unit to feed the nitrifying bacteria and help them proliferate. The steps involved have been outlined in Chapter 5 and they should be followed for every new unit.

During the cycling process, it is vital to test ammonia, nitrite and nitrate levels every 3-5 days to make sure the ammonia concentrations do not become harmful for bacteria (> 4 mg/litre). If they do, a water change is necessary. The unit has completed the cycling process when nitrate levels begin to rise and ammonia and nitrite levels fall close to zero.

Source: Food and Agriculture Organization of the United Nations, 2014, Christopher Somerville, Moti Cohen, Edoardo Pantanella, Austin Stankus and Alessandro Lovatelli, Small-scale aquaponic food production, Reproduced with permission.

Food and Agriculture Organization of the United Nations

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