yes that is the key, but a lot of people dont realize it is the problem. as far as ph I used to set my ph before adding nutes, I seen a lot of fluctuation in the ph not that some is bad but mine was what I thought to be eradict for the first two or three days after a res change. so for the hell of it I added my nutes first and then checked the ph and it was spot on 5.8 without using any down only adding the nutes. once I tried this my ph no longer makes large fluctuations. it always stays within tolerance. this brought me to a theory that if your using ph balanced nutes and ph up or down they actually fight each other before they balance out. I am not saying this is correct or that it is in any way scientifically a fact but just my experience and thought.