Yes, I am finding a lot of PH fluctuation. Even in the res. I filled it yesterday, and it is up 2 points today! I dont remember this kind of fluctuation using AN sensi grow and distilled water. Maybe I am one of the unlucky ones that experiences a lot of ph fluctuation with MC. I know that RO water can cause a lot of ph fluctuation....I was actually thinking my next grow of experimenting with just using my tap water and declorinating it, or for the hell of it trying distilled again..not sure. My poor PH pen has never seen this kind of abuse!