Remove the rind from the grapefruit and as much of the pith as you can and discard. Add the grapefruit to the base of a blender along with the strawberries and 2 tablespoons of the sweetener and blend until smooth.
Taste and add more sweetener as needed.
Pour the mixture into your popsicles molds and fill 3/4 of the way full. Freeze for 5-6 hours* (see notes) or until frozen through.