I think this is the most tricky to use, i have to use it 3 week before the Harvest (including the flush) so you have to calculate with the looking of the plant.
I make some reserch on the forum ands other information platform to find the best nutriments result on automatic plant and i have to say that the HESI product are (for me, in my experience) the best produc. I use the whole bundle of product for the PK equilibrating.