Marine industry is one of the strong sectors bringing great economic benefits in the world and especially in Vietnam. However, the control of marine aquatic environment is always a complicated problem in both solutions and implementation. Currently, monitoring systems are capable of measuring most of the indicators but still face many difficulties with special indicators such as NH3, H2S, which need to integrate many specialized equipment applications, complex measurement procedures, or waiting for results from a laboratory. Therefore, the implementation is hindered and increases the investment cost. In this article, the authors apply an indirect measurement method to determine the rate of ammonia (NH3) for an automatic monitoring system of the aquatic environment. The monitoring system will monitor the basic water indicators in the National technical regulation on aquaculture water including temperature, salinity, pH, and based on that to calculate and determine the distribution rate of NH3 – factor major cause of losses in the marine products industry. The application of this indirect measurement method aims to directly assess the fluctuation of the Ammonia NH3 index and contribute to the reduction of aquatic environmental monitoring models.