You will find a multitude of information as well as support in here, but I will be the first to advise you AGAINST any of the pre-mixed soils with regards to seedlings.

Believe me, I have killed my share of seedlings due to placing a perfectly prepared (tap root visible) seed into a pond of ammonia scum lol. Poor seedlings.

I am doing much better now that I have a more neutral soil (Jiffy-Mix seed starter) And so are my seedlings (which are starting to push through the surface) ^_^