How many days do you premix for water changes?

[Beverly]

We use about 30g of NSW for water changes in our three tanks each week. After the water changes, we clean and begin filling the two rubbermaid trashcans with RO/DI water for the next week's water change. Once each trashcan is full, we aerate it and heat it. The day before the water change, we add salt, mix it well with the pumps that have been aerating, and aerate and mix until the water change.