@nick8 , in soil a plant that young do not need fertilizer , just water them , and they will thank you .. some root stimulator if you want but no fertilizing unless you have a very very npk poor soil , and then when you transplant to vegging pots , depending on how long your veg will be you will or not need to fertilze.
As long as your roots are growing and entering new soil they will feed from it , forget about that "bulking" history , with good soil cannabis dont need nutrients at all during Veg unless you veg for too long , my plants only start to get nutrients at about 3/4 weeks after switch to 12/12 cause i make a transplant arrund 10 days before flowering..
Good Soil is way cheaper and gives you less troubles and your plants will thank you.