This work presents experimental observations on the permeation of multi-ionic solutions through a commercial DESAL-HL nanofiltration membrane. Two types of mixed-salt solutions have been analysed with a common co-ion (NaCl + Na2SO4) and with a common counter-ion ((NaCl + MgCl2)). The NaCl concentrations have been similar to those of seawater with divalent ions with lower concentrations up to a tenth of that of the monovalent salt. In this study. SEDE-VCh model that includes the variation of the charge inside the membrane pores has been used to model the system and structural, electrical and dielectrical membrane parameters for such systems have been obtained. We show that accurate enough predictions can be achieved for the retention of monovalent ions in the presence of counter or co-ion divalent ions from the single NaCl salt results. While correct predictions for the retention of the divalent ions require membrane charges and dielectric constants dependent of the ionic composition of the solutions filtered. (C) 2011 Elsevier B.V. All rights reserved.