Top-off system: This automatic water refill system helps maintain water level in your aquarium. For freshwater aquariums it keeps the water level constant so you don’t have to top it off manually, and for saltwater it does this, while also providing the added important benefit of keeping salinity very stable. Package comes with float switch/sensor, pump, power adapter, mounting bracket and hose. Recommended installation location is a remote sump. Pump requires a reservoir (not included).