Lot of pre fabricated soil tend to sneak in nutrients into their products. That combined with very wet soil and clohrine/chloramine water is a recipy for hair ripping. I actually went out of my house, dug up some sandy dirt from the basement and mixxed that with some basic soil from a park nearby. My seedlings loved it
When it comes to water, best water you can get is the rain that falls from the skies. It sounds silly, but many products imo takes away one problem and gives you another. Most weeds i've encounterd over the last year loves it when the soil is semi dry. Not that i think its overwaterd. I recently got a new soil type that i tested, and it didnt dry out before two weeks had gone by. heh..