Nutriens.

i usally start my feed at week 3 as the plant is developing itself. i give them a real small amount almost like a tease. this helps the plant get the right treatment from the start, in the first feed ill give some root enhancer. at this time in the young plants life i want to get those roots to grow, so you should prob. start a feed program in the up coming 3rd week of veg. hope that helps

Generally when the cotylodons start withering. (The two leaves that pops out of the shell.) They're nutrient banks for the seedling, and provide a good reserve for the plant in case it can't find any nutrients in the soil. So them withering is a sign.