Here at Top Shelf Aquatics, we believe that if you want a product that automates an aspect of tank maintenance, an ATO is the number one priority. Evaporation within a tank is inevitable, and the salinity of your aquarium will rise as a result of the salt that is left behind when that water evaporates. Your fish and coral will be lot healthier, and your protein skimmers and other equipment will work much better, provided the water level in your aquarium or sump is kept consistent. In order to transfer water from a reservoir to your aquarium, Auto Top Off Systems typically involve a controller that links to one or more sensors and a connection for a pump. Your aquarium's sensors will be able to detect when the water level is becoming too low, at which point the pump will start pumping fresh water into the aquarium until the correct water level is reached.