[Pavel Chaloupka]

Hello, somehow I missed this. Well I never really tried to compare such readings as I simply had the equipment. I knew I was going to measure pH in very low conductivity water so I bought the right electrode for that. Than I had no fish for couple years and sold all my laboratory devices that I had. When I started again I just bought normal stuff. How the electrode works is quite well explained for example here (not sure how much this helps 🙂 ): http://www.allaboutcircuits.com/vol_1/chpt_9/6.html. Anyways there are probably some parameters that need to be changed (type of membrane or electrolite) in water with that very low cunductivity as they infulence the readings for the standard electrodes too much in such environment and therefore the electrodes have to be adjusted.