You can be sure that the water in your aquarium is always at a healthy level thanks to the automatic EHEIM Refill+. Without a cover, water in aquariums is constantly evaporating. Because toxic chemicals (such as nitrate, among others) and metabolic products concentrate in the water, this is a serious issue that could endanger the lives of aquarium occupants. Another risk associated with marine water tanks is an increase in salinity (density). The evaporated water is automatically replenished by EHEIM Refill+. The water level is continuously measured by a sensor for this reason. Simply place the EHEIM Refill+ outside on the aquarium's glass pane, or, if the aquarium is filled with marine water, at the cabinet's filter tank (sump). When the water