Corrosion, scaling and biofouling are three problems in the power plant cooling system. In this paper, the influence of inhibitors and biocides on control of these problems for mild steel and copper-nickel alloys in a power plant cooling water system was investigated. The results showed that alone sodium hypochlorite (NaClO) in the presence of 1-Hydroxyethylidene-1,1-Diphosphonate (HEDP), maleic anhydride homopolymer (HPMA), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) as scaling inhibitors, and ZnSO4, 2-Mercaptobenzothiazole (MBT) as corrosion inhibitors was not effectively reduced corrosion, scaling and biofouling. In the presence of Alkyl Dimethyl Banzil Ammonium Chloride, one of the Quaternary Ammonium Compounds (QACs), the inhibition efficiency was increased. The effects of inhibitors on carbon steel copper-nickel were studied through electrochemical and weight loss measurement (C) 2015 Elsevier B.V. All rights reserved.