The aquaculture industry requires to change the water of fish aquarium every day to maintain high production quality. In this study, we assessed the use of the coagulation–flocculation process to treat fish-farm water with green coagulant concentrations (100, 300, and 500 mg/L) to remove turbidity, total suspended solid (TSS), and total dissolved solid (TDS). Phosphate (PO4) and nitrate (NO3) throughout the treatment were detected in fish-farm water, and Fourier transform infrared (FTIR) analyses were conducted for green coagulant and flocs. Jar tests revealed that the coagulants were able to reduce turbidity- 87%, TSS- 72.72%, and TDS- 8.33% and turbidity- 90%, TSS- 86.36%, and TDS-9.16% by palm pith and watermelon rinds respectively at a dosage of 100 mg/L. Through FTIR analyses, cellulosic materials were found in green coagulant which contributed to the efficacy of the coagulant. Additionally, phosphate increased in water owing to its release from palm pith and watermelon rinds, as confirmed by FTIR results. This study concluded that recovered nutrients and treated water contributed to the enhancement in plant growth as fertiliser and irrigation water.