Microorganism growth in industrial systems is controlled through the use of biocides and biodispersants. There is, however, no simple means of determining the efficacy of these control mechanisms, but it is currently tested using complex bacterial culturing techniques. Biolog Ecoplates® have been used to detect bacterial population changes in various communities. These microtitre plates comprise 31 different carbon substrates (in triplicate) with wells. When a sample is added to the wells, bacteria capable of metabolising the relevant carbon sources respire the substrates, causing the tetrazolium dye in the well to turn purple, indicating a positive result. Hypothetically, the higher the microbial diversity, the more substrates will be utilised and vice versa. The objective of this study was to test this hypothesis, using Biolog Ecoplates® as a potential simple indicator to determine the efficiency of a biocide to control microbial growth in cooling water systems by monitoring the changes in the microbial metabolic pattern. This study proved the hypothesis using Biolog Ecoplates®, indicating that the addition of biocides at various concentrations resulted in fewer substrates being utilised, indicative of a decrease in microbial species diversity.