I am trying this as well, on my current grow(s) at a dose between 0.2-0.4 grams in 500mls
I found a schedule which maximizes it's use, reducing waste.
Soak seeds for 10 minutes before planting- then spray all plants at 3 week intervals- so that's wk #3 & #6 in veg and #3 in flower.
I have not fed the roots with the left over solution, but will certainly look into it.