I do not use Superthive. Did years ago when I was a newbie. It's a vitamin/micronutrient additive that is okay if you don't have a feeding regiment from a more established nutrient line such as Botanicare (my personal favorite) or Advanced Nutrients, or even Foxfarm etc.. but if using Superthrive a few drops per gallon is plenty and recommended by anyone I know who has used the stuff. It has been known to cause strange leaf mutation and hermies in flower.. that is why I stay away from it. A more recommended additive that has been nothing but fantastic in my experience is Botanicare's Liquid Karma. 10ml per gal for cuttings. It is a seaweed extract based nutrient that also contains Vitamin B.. has proven results with getting clones to root faster, quicker, and at a higher success rate. To apply, mix in a one gallon container, pour in a clean plastic sprayer and mist soon to be clones once every 2 days in a humidity dome. Before placing cuttings in dome, I soak my rapid rooters prior to taking the cuts in a solution of Liquid Karma 5ml per gal with plain distilled water (only a buck a gallon at the grocery store).
My clones usually come out at 90% success survival rate, usually 9 outta 10.