Salt gradient solar pond is one of the methods for absorbing and storing solar energy. This study investigates experimentally the performance of mixed medium at the lower convection zone of laboratory scale solar pond. The experiment was carried out in Dezful, Iran. This specific geographical location mainly has a high-level of solar radiation and intense dusty climate. The climatic condition criterion and mixed medium distinguishes the novelty of this research. Data was obtained in 90 days period for the temperature distribution and salinity gradient. For comparison, two similar solar ponds of circular cross section with surface area of 0.51 m(2) and height of 63 cm were designed and built. Two layers of pebble and ball bearing as porous medium were used for one of the solar ponds in the lower convection zone (LCZ). At the end of test period, the temperatures of mixed medium and conventional in the lower convection were obtained at 75 degrees C and 71 degrees C, respectively. Therefore, the mixed medium solar pond indicated an increase of 5.6% in temperature. In addition, variation of maximum temperature of the mixed medium pond was less than the conventional LCZ solar pond. Using the mixed medium in the LCZ resulted in more thermal stability and lower temperature drop. However, mixed medium indicated higher thermal resistance and more storage capacity for the pond. Non-dimensional numbers have been introduced for the optimization of this mixed medium condition. A criterion parameter has been obtained for the optimization of the mixed medium in the solar pond. (C) 2017 Elsevier Ltd. All rights reserved.