The Eheim waterrefill automatic refilling device is a water level control for aquariums, which is used for refilling vaporised aquarium water automatically. Eheim waterrefill not only adapts automatically to the size of your aquarium, but also to the seasonal changes on the site of installation. The sensors used by Eheim offer many advantages: Due to their position outside the aquarium, the sensors cannot become dirty and are not blocked by aquatic plants and/or creatures. In addition, the sensors can be used at optional high and also at shallow water levels and in extremely soft up to very hard sweet as well as sea water.Eheim waterrefill+ automatic refilling of evaporated water+ perfect during holidays+ the sensor with LED display is permanently measuring the water level+ fastening of the sensor easily accessible outside of the glass pane of the aquarium+ in case of a marine water tank alternatively at the filter tank in the cabinet (sump)+ works with most common glass thicknesses 4