i've used GH 3 part through a few grows and will try to help.
my experience is limited to hydro but most of the info should translate well to soil.
if you are using tap water, you should keep your PPM very low (never over a 1000 PPM at most).
The strain can really determine how much nutrients the plant can take. Some strains can handle very high levels of PPM - but just because it can "handle" it doesn't mean it thrives that way.
as a general rule (your mileage may vary)..
no nutes until about 2 - 3 weeks old. in hydro - i actually start adding nutes the first week but keep it under 2-300PPM
So week 0-4 - under 300PPM
week 4-5 under 500 PPM
week 6 (transition to 12/12) back to 300PPM
week 7- 9 under 700 PPM
rest of grow under 1000 PPM
Note that some strains may not like anything over 300 or 500 PPM - so watch the plants!
This assumes switching to 12/12 during week 6 but you can adjust your time accordingly.
was this what you were looking for?
as for which nutes and how much - i use the GH feeding guidelines for ratio but reduce the amount. Does that make sense?