The objectives of this study were to prove the control of the lake water quality in terms of turbidity, total suspended solid (TSS), chemical oxygen demand (COD), and number of the algal cells by using the Riplox-based chemical complex (including (Ca(NO3)2) and (FeCl3) at concentrations ranging from 5 mM to 50 mM, with the presence of CuSO4 4 mg/L), considering the effects of the chemical fraction, the chemical concentration, and the treatment time. Raw water was sampled from Trieu Khuc Lake and treatment process was carried out in the lab scale. Overall, the great treatment results were achieved from the application of Ca(NO3)2/FeCl3 ratio of 1:1 (v/v) at a concentration of 0.5 M and the treatment time of 3 hours. The presence of CuSO4 4 mg/L in the Riplox-based chemical complex showed a good performance in reduction of number of the algal cells. The flocs formation when dissolving Ca(NO3)2 and FeCl3 in the water and denitrification were found to be major mechanisms for enhancing treatment performance. The findings demonstrate that the application of Riplox-based chemical complex with the presence of CuSO4 4 mg/L would control the urban lake water quality and can be widely applied for the case of Vietnam