The HYDROS DC Solenoid Water Valve is a crucial accessory for HYDROS Control 2 and Control 4 systems, designed to automate the on/off flow of RO or RO/DI water. It functions as an essential component for auto top-off (ATO) applications, allowing reef keepers to maintain stable water levels in their display tank or sump without needing a separate ATO reservoir. This valve integrates seamlessly with a HYDROS aquarium controller and an optical or mechanical water level sensor to precisely manage water replenishment. When a water level sensor detects a low water level, it signals the HYDROS controller to open the valve, allowing fresh RO or RO/DI water to flow. Once the sensor detects that the water level is replenished, the controller shuts off power to the solenoid, closing the valve and stopping the flow of water. This device should be connected to the product line coming off your reverse osmosis system and features 1/4" push-connect fittings for quick and easy insertion of standard RO tubing. This solenoid valve is ideal for saltwater aquarium enthusiasts utilizing a HYDROS Control 2 or Control 4 system who seek a precise and space-saving solution for automated top-off. It caters to those who prefer direct RO/DI line integration over a traditional ATO pump and reservoir setup, ensuring consistent water parameters. This product is perfect for reefers aiming for advanced, integrated control over their aquarium's water level management and overall stability.