3/4 cup fresh lime juice (from about 8 limes), plus wedges for garnish
Combine the sugar, hibiscus and 1 cup water in a small saucepan. Bring to a boil, reduce the heat to medium and cook, stirring occasionally, until the sugar is dissolved. Transfer to a small bowl and refrigerate until cold, at least 1 hour.
Combine the tequila, triple sec and lime juice in a pitcher. Strain the hibiscus syrup into the pitcher; stir until incorporated. Chill 30 more minutes.
Spread some salt on a shallow dish. Moisten the rims of 8 glasses with a lime wedge and dip in the salt. Combine half of the tequila mixture with 4 cups ice in a blender and blend until slushy. Transfer to a separate pitcher; repeat with the remaining tequila mixture and 4 more cups ice. Serve in the prepared glasses; garnish with lime wedges.