If my PPM are 450 going in what is the range they should be when it comes out
What stage of growth?
How old are plants?
How big of a pot?
What kind of soil are they in?
Answer those questions and then you can start to figure out where your ppm’s should be… 
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Yeah def need to know all the aspects before making a decision soil is around 6.5 if using a dwc system then u flush everything out for a week at the end