In a bowl, whisk together both juices with honey and salt. Add in tonic water. Taste and adjust sweetness to your liking.
Pour the liquid into a 10 x 10 casserole dish and place it into the freezer.
Place in freezer for an hour.
Remove from the freezer and stir liquid with a fork. Place it back into the freezer for another hour.
Remove and stir again, breaking up and big frozen chunks with a fork.
Place back into the freezer for another half hour. Serve in a chilled glass with a sprig of mint on top.