Water quality affects the health level of fish, one of parameters that must be maintained is ammonia levels. Ammonia levels which are left high will be harmful to the health of fish. In this study, a control and monitoring system on ammonia level for fish cultivation has been designed that are also useful for measuring the quality of water in an aquarium. Measurements conducted on this study have two main variables, namely pH and ammonia levels. Two sensors namely pH sensor and MQ-135 gas sensor are used equipped with Arduino microcontroller as a controller and data acquisition. Raspberry Pi 3B as Single Board Computer is utilized as processor and serves as Internet of Things (IoT). In the system, the pH is kept neutral (6.5 - 7.5). When the value exceeds the limit, automatic control will channel the liquid acetic acid (CH3COOH) to the aquarium to balance pH level. The results of the tests show that the system can perform controls automatically and manually. The measurement of pH sensor data has an average error of 1.88%. Manual monitoring and control of on- and off-conditions of aerators and water filters have a 10-second delay. Manual control and monitoring is carried out through a smartphone application so that it can immediately inform if there is an increase in pH and ammonia levels which can harm the fish.