In the present work, experiments were carried out to investigate the effect of sealant and antiscalant concentrations on fouling in a desalination unit using the solar multiple condensation evaporation cycle principle. Synthetic solutions equivalent to those of feed water obtained after different condensation-evaporation cycles were used. Kinetic and thermodynamic analyses were established to explain the gypsum precipitation with varied feed water concentrations in salts. It was shown that, the saturation level and therefore calcium sulphate precipitation rate increased with operating time. The solubility of CaSO4 center dot 2H(2)O increased with increasing the ionic strength and the saturated solutions kept metastable equilibria for saturation level of similar to 2.5. To prevent gypsum formation, different concentrations of poly(acrylate) were used. This antiscalant strongly affected the precipitation rate, the texture and the morphology of gypsum. (c) 2006 Elsevier B.V. All rights reserved.