hey black BX....
unlike what was spoken of hydro methods and ppm recipies, DWC and RDWC have everything to do with PPMs.
knowledge is key here where expierence comes into play.
I run an ebb and flo with hydroton...my medium is saturated for less than 10 minutes fully every 4 hrs.
the roots are not in solution 100 percent of the time...therefor can take the higher ppms in my feed schedule.
being in an rdwc you ppms WILL be lower....
are you feeding with an R/O solution where your ppm start is low??
if so you will DEFINATELY see a lower ppm starting out t hen someone who says they mix this ratio with this (with the same amt of nutes)in thier tap water and get this high ppm from the get go.
what you need to look for is any sign of nute burn being in your rdwc.
it could burn at 900 ppm could be 1200...
watch the plants and you will find what they like.
bumping up the ppm will find you pleasure i promise.
EDIT- PLEASE UNDERSTAND THAT - less is more in the beginning!!!!!