A metal halide fill for a discharge lamp is provided that is comprised of mercury and a mixture of metal halide salts which includes magnesium iodide as a full or partial replacement for calcium iodide. The replacement of at least some of the calcium iodide improves the behavior of the molten salt condensate in the arc tube. In particular, the mixture of metal halide salts contains about 1 to about 50 mole percent sodium iodide, about 15 to about 50 mole percent of a rare earth iodide, about 10 to about 30 mole percent magnesium iodide, about 10 to about 25 mole percent of indium iodide, and about 0 to about 25 mole percent calcium iodide, wherein the sum of the amounts of calcium iodide and magnesium iodide in the mixture is from about 20 to about 45 mole percent.