I think when you are referring to "20 ppm" for example, you meant to say "TDS" ... ?? ... a typical hydroponic grow when expressed in ppm would be '1350 ppm' , etc ... I apologize if I've misunderstood, but your numbers are way different than mine (I know there are 2 kinds of meters, but that's all I know) :jointsmile: (sorry, I'm confused)