I couldn't get anywhere near that high with my system. If the ppm is too high the ph drops, and that's what happens when I get to 350 and I'm in flower. I believe it has to do with the amount of air in the system. Lots of air, less ppm. Of course that's how I understand it. Someone chime in and let me know if I'm correct.850ppm... awfully high for small plant...do you run that high all the time?