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In aquaponics, it is very important that the input and output of nutrients is in balance over the entire plant growing period. This balance can mainly be controlled using two different approaches:
Approach 1: An existing recirculating aquaculture system (RAS) is used to dimension the corresponding hydroponic unit with plants (Figure 12). This approach is covered by the Exercise in Module 5 (nutrient water balance).
Approach 2: The RAS is dimensioned based on the desired plant and fish production (Figure 13). This is covered by the in Exercise in Module 2.
The aim of dimensioning the RAS part of an aquaponic system is to adjust the different water treatment stages in order to achieve both good water quality for the fish, and sufficient nutrient supply for the plants. It is always an advantage if the system is as unaffected as possible by seasonal fluctuations (temperature, dissolved oxygen, ammonium, nitrite and nitrate). In general, it can be said that a large water volume and low stocking densities make systems more stable. It is important that the whole year is planned and that differences in the fish and plant species as well as the growth stages of all species are taken into account. As support for this planning, it is recommended that the 'Planning Basis for Dimensioning the Recirculating Aquaculture Part of an Aquaponic system model’ is used (Tschudi 2018).
Figure 12: Dimensioning of the plant nutrient uptake based on existing RAS dimensions
Figure 13: Desired plant and fish production and corresponding dimensioning of the RAS
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