Best bet is... buy new one, and throw used soil in garden/compost.
When plant takes nutrient from soil at different rate, it's no longer the same soil so you're asking for troubles. Let's say your plant eats whole iron and magnesium from soil and not so much other minerals. What will happen when you'll put another plant in this soil? You have the answer.
I always re use soil with great results. Its best to let the soil stand/cook for a month or 2 before reusing so that the bacteria in the soils can do their magic and replenish the nutrients.
Let's face it whatever soil we use is always going to be different in term of less/more in terms of certain nutrients and thats where our work comes in to play. Spot the signs early and give the plants what they are looking for.