When you have 2 or more species, the Concentration Display menu should show Select Pollutant: All, SPE1, SPE2, etc. When you choose SPE1 or SPE2, then the plot should be only for that one (labeled on the output graphic just above the map). When you choose ALL, all species' concentrations are summed, and the label says "SUM Release...".
To verify your output file has 2 species, run Concentration / Utilities / Simple listing. It should show Number and ID - 2 SPE1 SPE2 and give the min and max concentrations for both species on each output level.
Make sure the 2 species have different 4-character IDs.