You don't want to premix nutes and leave them in a jug. The various salts can precipitate and form solids. That's why liquid nutrients in concentration come in different bottles. You can store unused mixed nutes in some kind of reservoir with aeration or a small pond pump on the bottom to keep the solution moving around preventing precipitation of the salts. That's what hydro growers do.
What is a Precipitate?
In chemistry, a precipitate is an
insoluble solid that emerges from a liquid
solution. The emergence of the insoluble solid from solution is called precipitation. Often the precipitate emerges as a
suspension.
Precipitates can form when two soluble salts react in solution to form one or more insoluble products.
soluble salt 1 + soluble salt 2 → insoluble salt (precipitate)
https://www.chemicool.com/definition/precipitate.html