When you are just doing top offs, topping off evaporated water, you just use plain water. Salt does not evaporate with the water, so if you added salt to evey top off, your salinity would go through the roof in very short time.
You mix up a normal batch of salt water when you are planning on doing your maintenance water change.
forum community dedicated to tropical fish owners and enthusiasts. Come join the discussion about species,breeding, health, behavior, aquariums, adopting, care, classifieds, and more! Open to fish, plants and reptiles living in freshwater or saltwater environments.