Well, for IO, etc., it isn't just open and pour as you should be aware of the way the salt settles during transport. Meaning that the salt mix isn't the same throughout the bag or box and should be mixed or stirred prior to adding to water. This isn't so important for FOWLR tanks, but I have all Acropora and like to keep conditions as ideal and stable as possible. YMMV I also do not change salts and try to use the same each time as Alk, Ca and Mg can vary widely between brands.