The effect of salt additives on the potentiometric response of solvent polymeric membrane pH electrodes based on the electrically charged carrier 4’,5’-dibromofluorescein octadecylester (ETH 7075) is evaluated. The incorporation of potassium tetrakis(p-chlorophenyl)borate as anionic site forces the carrier to reveal its weakly basic properties, only showing a Nernstian pH response below pH 2.5 in 0.1 M KCl. In contrast, the presence of tridodecylmethylammonium chloride as cationic sites induces an electrode function that reflects the analytically useful acidic characteristics of the carrier. The latter system shows a pH measuring range between pH 3.5 and 10 and a selectivity coefficient over potassium of log(HK)(pot)= -8.3. The differences in response behavior are explained qualitatively on the basis of the phase boundary potential model.