The inhibition efficiency of 4-amino-5-methyl-4H-1,2,4-triazole-3-thiol compound was studied by itself as well as in a mixture that included co-additives (polycarboxylate and citrate) for C1010 steel in a typical ground cooling water environment. Weight loss measurements, solution assay analysis, electrochemical impedance spectroscopy and potentiodynamic measurement techniques were utilized for the assessment of corrosion inhibition efficiency. The inhibition efficiency was found to be 70%, with 100ppm inhibitor concentration, without any co-additive. This case was attributed to limited access of existing inhibitor molecules on the surface in the presence of various insoluble compounds that are readily formed with various cations and OH- ions. In order to prevent scale deposition and strengthening of the inhibition efficiency, polycarboxylate was used as the dispersive agent and citrate ions were introduced for synergism. The SEM-EDS analysis clearly depicted that the mixture formulation (10ppm 4-amino-5-methyl-4H-1,2,4-triazole-3-thiol+1ppm polycarboxylate+2ppm citrate) could prevent scale deposition and the attack of corrosive environment. Furthermore, the inhibition efficiency of this mixture was determined to be 89%. FTIR studies indicated the presence of both 4-amino-5-methyl-4H-1,2,4-triazole-3-thiol and citrate in the protective surface layer.