I have two nano tanks (waterbox mini 15 , evo 13.5) Both have open tops and evaporation issues.I have a fz ATO but I'm confused about it's usefulness. In order for the sensor to register that the water level has dropped i'd have to lose enough water to make my salinity rise more than I think is safe. Am I better off just topping off with fresh ro water manually each day or maybe twice a day? I've read that even a slight change in salinity will negatively effect corals and the general health of the tank?