Ok, running straight waters PH 5.7 PPM 400. Roots are lilly white and massive. Let me put this in perspective, I have had the same setup for 4 years and only have had a total wipe out once 3 years ago and did not know the reason. Do about 4 to 5 grows a year and haven't changed lighting or highth of lights, chemical products have not changed and using GH by the book as I have done all along. Have not changed anything but differant plants. These are the same plants for the last 3 grows. This system is not small, I have 42 holes, 8' tubes, 4 1000 HPS lights and a 50 gal res. I am just trying to figure out what I have done wrong as maybe not cleaning out enough between grows, something got in the system, I just am dumbfounded and don't want to lose this one. Maybe this will help some, I hope.