Scaling aquaponic systems: Balancing plant uptake with fish output

•A simple new method to size aquaponic systems is described.•Plant crops differ in dissolved inorganic N species preference and nutrient removal capacity.•Nutrient removal variable over cropping interval with highest rates when plants are young.

To be effective at nutrient removal, aquaponics systems should be sized correctly to balance nutrient production from fish culture and nutrient uptake by plants. We describe a method where the plant component was isolated from the fish rearing operation so that nutrient removal could be evaluated independently. Two crops, lettuce (Latuca sativa) and nasturtium (Tropaeolum majus), were evaluated. Nasturtium had higher removal rates and removed both total ammonia nitrogen (TAN) and nitrate resulting in 80% DIN removal while lettuce removed only 48%. Lettuce removed only TAN and was ineffective at nitrate removal. Older plants were more effective at DIN removal while younger plants were more effective at PO4 removal. When normalized for biomass, younger plants had much higher removal rates. These results demonstrated that both crop and cropping method have considerable impacts on nutrient removal. This method will allow operators to adjust their system quickly and easily to meet remediation goals.