Step by Step: Bring 1-2 gallons of water to 180°F and stir in dextrose to dissolve. Bring sugar-water mixture to a gentle boil for 5-10 minutes, then stir in Propper Nutrients. In a sanitized fermenter add a gallon of cold water and pour in the sugar-water mixing thoroughly. Top up the fermenter to 5.25 gallons with additional cold water until the resulting base is approx. 68-80°F, pitch the yeast.
After 4-7 days check the specific gravity of your seltzer. When final gravity is reached add flavoring(s) to taste and bottle or keg as desired.