i think what thehempgoddess was getting at is that dwc is almost plant/strain specific as far as nute/ph/ppm/etc regimen...
...some plant strains like it hard, some like it soft. ya dig?
most of the time you want to try to put the same plants/strain in the same res and try not to mix strains. ...i've seen mixed strains work on an ebb/flow system with success. i've seen mixed strains work in a dws same-res system, too...don't get me wrong. it's just not advised.
prime example is my outdoor grow...my chemdawgXsourdiesel plant is a nute-wh0re. she can't get enough. ...my presidential kush plants on the other hand barely need/want anything at all. if i had them in the same res, one or the other strain would eventually fail.
peace,
mr_chow