Your soil is a prefertilised soil=?. Normally you dont have to feed your seedlings before they 4 weeks old / or before if they show defiencies. Using a good prefertilised soil (BIOBIZZ/ Plagron) or something helps you for weeks. If your plant should show defiency(yellowing etc) you can start with half or 1/3 amount of the fertiliser, and look how the plant reacts. Then its good if you have a shedule for feeding and watering.. and like always less is more, A defiency can aplant handle. An excess can kill her... Happy growing. dare to ask more