From their website:
Botanicare : FAQs
Q: What should my ppm read during each phase of growth?
A: It is hard to get true reading when using organic nutrients. When using inorganic salts this is a general ppm guideline: Seedlings 500 ppm Mid Size 900 ppm Mature 1300 ppm Fruiting/Flowering 1500 ppm Aggressive 1800 ppm Super Aggressive 2400 ppm