Monitoring water tank levels can be tricky and gauges are essential on boats. Some tanks must stay full while other tanks need to be bled as the gauge creeps up. A wide variety of single level gauges available at Defender are designed to monitor water tank levels in individual tanks. LED panel marine tank monitor systems and sensors do the same thing in multiples. Monitors basically offer one base for keeping an eye on all your tanks at the flip of a switch - even at night!