Recirculating Aquaculture Systems (RAS) have increasingly gained attention in Bangladesh due to their efficient water use. However, maintaining real-time water quality is challenging, as delayed anomaly detection often causes economic loss and compromises fish health. To address this, we developed a low-cost IoT-based monitoring and alert system that integrates industry-standard sensors to track key water parameters (pH, turbidity, dissolved oxygen, temperature, oxidation-reduction po- tential, total dissolved solids, and electrical conductivity) using Arduino microcontrollers and ESP8266 Wi-Fi modules. The total hardware cost was under USD 700, an order of magnitude cheaper than commercial systems. Sensor readings were published every 15 s via MQTT to the ThingSpeak cloud platform, enabling real-time visualization and WhatsApp-based alerts for immediate intervention. Experimental deploy- ment demonstrated the system’s capability to maintain optimal conditions consistently, identifying critical events such as abnormal water quality drops efficiently. Clear daily and monthly trends were observed, enabling predictive adjustments and informed automated decision-making. This IoT approach significantly improves operational efficiency and reliability in resource-limited aquaculture settings typical of Bangladesh, ensuring sustained fish productivity and welfare.