Pilot-Scale Evaluation of Coral Reef Media for pH Buffering and Nutrient Supply in Koi-Lettuce Aquaponics

Nutrient deficiencies and pH fluctuations are among the major issues identified in most aquaponic studies. Studies have mainly used chemical fertilizers and pH adjusters to resolve these issues; however, a sustainable and environment friendly permanent solution is needed. In this novel pilot study, we incorporated coral carbonate media into a koi carp-lettuce aquaponic system-A (APA) to provide a continuous release of Ca2+, Mg2+, Fe, and P and to support accumulation in plant and fish biomass while maintaining neutral pH, in order to compare with the control aquaponic-B (APB). In APA, mean FCR, SGR, and PER were recorded as 1.57 kg feed·kg fish−1, 0.58%·day−1, and 1.77 kg feed·kg fish−1 protein, respectively, in comparison with the control APB which showed mean FCR, SGR, and PER as 3.45 kg feed·kg fish−1, 0.27%·day−1, and 0.80 kg fish·kg protein−1, respectively. Also, the mean plant mass obtained during this 28-day study was 5.28 and 4.40 kg with a fish weight gain of 0.51 and 0.22 kg for APA and APB, respectively. In this pilot-scale study (n = 2 independent systems per treatment), the observed plant and fish biomass in APA were 20.9% and 10.1% higher respectively than APB; these values show descriptive differences observed in this study. Nutrient analysis was found to show higher release and accumulation of key nutrients in APA. This study examined a low-chemical, sustainable approach for aquaponics by using reusable coral carbonate media to maintain neutral pH and to improve nutrient availability and productivity.