Mg2+ and the corresponding Mg(OH), play roles in the transformation of calcareous deposits in sea water. In this paper, only Mg(OH)(2) deposition is considered. The composition of other components involved (except Ca2+ ions) also follows ASTM standards. A model of Mg(OH)(2) film formation is presented by considering this film as a porous layer. The basic technique to investigate the Mg(OH)(2) film formation has been chronoamperometry used in conjunction with ac impedance and EHD impedance techniques to complement the information about the morphology of the magnesium hydroxide deposit. (C) 2000 Elsevier Science Ltd. All rights reserved.