Slice Grapefruit into 1/4 inch rounds. (Discard ends and any slices that have too much pith.).
Place all ingredients in a saute pan and bring to a boil.
Boil gently for 5 minutes, stirring intermittently. (I used a fork to make sure the fruit slices were stirred around evenly and changed them up from top to bottom a bit to ensure all were cooked into the mix thoroughly.).
Remove from heat and remove grapefruit slices, squeezing gently to get out most of the juice.
Mix 1/2 Cup of the syrup with 1 Liter of carbonated water.
Store remaining syrup in bottle or airtight container.