Slice celery and cucumber into 1/2 inch slices. Add celery and salt to cocktail shaker and muddle until broken up. Add cucumber and agave nectar, muddle until smashed, about 20 seconds. Add lime juice and Exotico® Blanco Tequila to shaker and fill 2/3 full with ice. Shake until well chilled, about 20 seconds. Strain into highball glass. Top with seltzer, stir gently and serve with cucumber slice garnish if desired.