Effect of K⁺ and Mg²⁺ in water on the performance of Litopenaeus vannamei using bioflocs was evaluated. Control had water with K:Mg (1:4.57) and other treatments (K:Mg of 1:5.4, 1:4.65, and 1:3.77), both with salinity of 4 g/L. Initial mean weight of shrimp was 0.08 ± 0.007 g. No difference in shrimp growth performance and survival was observed (P > 0.05) except in the control. Our results suggest that it is possible to culture postlarvae of Litopenaeus vannamei in low-salinity water with bioflocs when the water has an initial potassium concentration of 30.90 ± 8.5 mg/L and magnesium of 167.0 ± 3.9 mg/L.