Aquaculture wastewater contains high levels of organic matter and nutrients, which can be harmful to aquatic life if discharged improperly into surface water bodies. Coagulation-flocculation is currently the best practice for treating aquaculture effluent with biocoagulants, offering an alternative to metal-based coagulants. This study aims to investigate the potential of Tamarindus indica seeds as a biocoagulant for treating aquaculture wastewater, focusing on the optimal solvent extraction, concentration, and dose. This study also examines the toxicity of biocoagulants to aquatic organisms. Coagulation-flocculation study was conducted under jar test experiment with NaCl, NaOH, and HCl used as solvents; concentration of 0-10 g/L; and doses of 1-5 % v/v under 120 rpm (rotation per minute) rapid mixing for 1 min, 20 rpm slow mixing for 20 mins, and 60 mins sedimentation time. A characterization study showed that NaCl-treated T. indica has a positive zeta potential charge, attributed to the presence of hydroxyl, carbonyl, and amide functional groups. Under this optimum condition (NaCl-extract, 6 g/L, and 4 % v/v), the biocoagulant achieved high removal (>50 %) of turbidity, TSS (total suspended solid), and ammonia and considerably good removal of other parameters (TN [total nitrogen], BOD5 [biological oxygen demand], COD [chemical oxygen demand]). The toxicity test revealed that no mortality was observed at a concentration of 1 g/L, whereas 10 g/L resulted in a 100 % mortality rate after 24 hours of exposure. Further toxicity analysis is suggested to be conducted using treated final effluent (not directly using biocoagulant substances) to observe the direct impact of the treated wastewater if discharged into the water bodies.