Lime juice (fresh)
Grapefruit juice (fresh)
Add tequila, simple syrup, freshly squeezed grapefruit juice, freshly squeezed lime juice to a shaker and fill with ice.
Shake ingredients for 15-20 seconds, or until chilled.
Rim your shot glasses with salt and strain tequila mixture evenly between shot glasses, filling it up about 2/3rds full.
Top off with club soda & enjoy!