you should not fertilize plants that are so young. wait until the plants are on their 5th node (5th set of "true" leaves - the pointy ones, not the small circular ones that came out first). once they are on their 5th node, transplant to a larger container and you can fertilize with whatever type you want. Just remember that the fertilizer should be higher in nitrogen than phosphorus or potassium for that stage of growth. Once you decide to induce flowering (im assuming this is indoor) re-pot again and add fertilizer that is higher in phosphorus and relatively low in nitrogen. Does that help at all?