Hi Sence8,
I use to grow in soil and there is no way of knowing what's in it, as it can vary so much, even bag to bag from same supplier. Going more expensive does not necessarily solve the problem. and some soils are more expensive that a growing medium. Yes you can follow the link above and yes I've tried playing around as stated, however its still so difficult to get the neuts correct. Never lone how to get the nitrogen out of the soil as its usually far richer in nitrogen than a grow medium. I was not convinced that a medium was the way to go but you can now control everything and plants respond accordingly. I also found with Autos that the PH has to be 6.5 and not between 6 and 6.2 as for periods.
Happy growing