Keep them moist at this stage. You should keep the soil around 6.1-6.5 ph. Also, keep them moist with the light in their faces. At this stage (the last pics posted) you don't want to nute them yet. I would wait until the second or third set of true leaves. Fox Farm Grow Big 6-4-4 would be a good choice. As you mentioned the local store carries Tiger Bloom, this is the same brand but, for flowering stage. Fox Farm is a trusted product the Grow Big is for this early vegatative state.

Do you know the strain?

cheers,