<![CDATA[Maintaining stable water quality is essential for sustainable tilapia aquaculture, yet conventional monitoring often relies on periodic measurements and provides limited capability for automatic environmental regulation. This study presents a prototype Internet of Things (IoT)-based system for multi-parameter water-quality monitoring and local temperature control using an ESP32-S3 microcontroller, DS18B20 temperature sensor, pH-4502C sensor, SEN0189 turbidity sensor, relay-driven water heater, and Blynk cloud platform. The system acquires temperature, pH, and turbidity data at 5-s intervals and integrates local autonomous control with cloud-based supervisory monitoring. A hysteresis-based ON–OFF controller activates the heater below 27.5 °C and deactivates it above 30 °C, while the Blynk platform provides real-time visualization, historical monitoring, and notification functions. Experimental evaluation included sensor calibration, communication performance testing, temperature-control evaluation, and integrated functional testing under seven operating scenarios, with each scenario repeated three times. The DS18B20 achieved a mean absolute error of 0.175 °C, while the pH sensor exhibited a mean absolute deviation of 0.103 pH units and a maximum deviation of 0.12 pH units across the tested buffer solutions. Turbidity was qualitatively classified into clear, turbid, and highly turbid conditions. The communication subsystem achieved an average end-to-end latency of approximately 1.0 s, with no packet loss observed under the tested connected-network condition. The results demonstrate the feasibility of integrating multi-parameter sensing, autonomous temperature regulation, cloud monitoring, and notification within a cyber-physical prototype for laboratory-scale tilapia aquaculture monitoring.]]>
