In a drinking glass, add the fresh squeezed grapefruit juice, chamomile simple syrup (add more or less to taste), tequila and blackberries. Using a muddler or wooden spoon, gently crush the blackberries until they release their juices. Strain the mixture through a fine mesh strainer to remove the blackberry seeds, if desired. Add desired amount of crushed ice and top off with the sparkling water. Give the drink a stir, adding more simple syrup or fresh grapefruit juice as desired. Garnish with a few springs of fresh chamomile flowers and blackberries. Drink and enjoy!