Ca(+)/H(+) antiporter that extrudes calcium in exchange for external protons. Plays an important role in salt tolerance. Does not transport sodium or lithium. Optimum pH is 8.0. Disruption causes the rapid degradation of pigments and salt-sensitive phenotype at alkaline pH. Belongs to the Ca(2+):cation antiporter (CaCA) (TC 2.A.19) family. Cation/proton exchanger (CAX) subfamily.