I use in a diluted solution for soaking seeds and sprouting/germinating. Be carefull though it is some strong shit and smells bad like super ferts. also
1ml/gallon is recommended but that is some strong solution for seedlings.They will die right before you eyes. I mix at about 1/4 strength.
In the veg cycle I use full strength (1ml/gallon) in my veg cycle but only the first couple of weeks. It seems to give everthing a good head start, very robust and stress tollerant plants. None in my flower stage at all. All hydro is my thing no soil so I can't speak about soil.
I stop after the first couple of weeks because I am trying to stay as close to organic as possible and superthrive is anything but organic. Hell it smells like a "Chem Lawn" truck right out of the bottle so I use it sparingly.
I use it in conjunction with Pure Blend Pro nute program.
Hope this is a little help