In large pitcher, stir together grapefruit juice and pomegranate juice.
Chill at least 2 hours or up to 24 hours.
Just before serving, stir in ginger ale and orange slices into the grapefruit-pomegranate mixture.
If you are using fresh grapefruits and juicing yourself, it would be about 4 grapefruits to equal 3 ½ cups of juice depending on the size of the grapefruits. You could also substitute orange juice for a different twist on this recipe.