[Pavel Chaloupka]

Also try to check your pH meter calibration, if your measurements are correct. Measuring in very low conductivity environments as we do with Paros will often lead to dilution of KCl solution in the electrode, so proper storing of the electrode in the 3M KCL storage solution and its frequent changes as well as frequent calibration should be matter of course. I have just checked my pH meter after approximately 3 weeks of frequent measuring and I was getting an error of about 0,4, so it seems like I have to check the calibration even more often. When measuring waters with higher volume of dissolved substances and higher pH, the calibration usually lasts much longer, at least for me.