Question: Do I Add Salt or Fresh Top-Off Water?
When the water level drops in my saltwater aquarium, am I supposed to add salt or fresh top-off water?
Answer: When the water in a saltwater aquarium drops, it is primarily the freshwater that has evaporated. When adding top-off water to the tank, it is the freshwater that needs to be replenished. However, one has to test the tank's specific gravity or salinity regularly, because over time salt is lost, typically due to salt creep, so some new saltwater will have to be added when needed.