Im currently in a 12/12 form seed grow, and I'm wondering when to start nutrients. To see my progress look at my journal link in my signature (I'm now on day 20)
At almost 2 weeks I start with 50 ppm grow mixture and up it every dosing by 25 ppm. I use fox farm ocean forest mixed with fox farm light warrior soil 50/50. My soil has nutes in it but I see yellowing from nitrogen deficiency right around 2 weeks.
I give my Russian comfrey fert, which I know is 100% organic, to my sprouts when they show their first single finger leaves. When they show 5 fingers I add some BioCanna.