Try to go organic in all things, soil, ferts, and additives. Make sure your grow space has reflective material in it and there is no light leakage whatsoever. When and if you get some superthrive only use it during vegetative stage. It doesn't do much and in some cases inhibites floral growth. Use sugar doing flowering instead. Try to give your soil a good N count cause higher N levels at the begining of growth helps to promote female tendencies. As for lighting go for a 20/4. Another thing, make sure the circuit you are putting the HPS on can support it. You don't want the house to burn to the ground do you? A good light mix for two plants is three Cool watt CFL on each plant with one Warm CFL over both to help fill out the spectrum. Hope any of this helps.

Happy Toking :rasta: