P.C. can be a difficult grow and although people rave about the smoke, it's a difficult grow for most. Red stems are typically a sign of a phosphorus deficiency, not nitrogen. If you use a R.O. device, you must always add cal/mag thru the grow as it's takes whatever cal/mag normally in the water out. Usually it's 5ml per gallon but R.O. users should use 10ml til mid way thru flowering. And P.C. is a stink bomb........