Put all the ingredients into an airtight container.
Stir or shake to blend well.
Keep airtight; in humid climates, tuck in a silica gel packet to stop clumping.
Notes
1-2 tablespoons in the detergent cup; set a shallow dish of white vinegar on the top rack to help prevent spots; run as usual. Adjust for water hardness (with very hard water, add the citric acid separately or use vinegar). A mason jar with a pour spout works well.Safety: wear gloves; keep away from kids and pets and label it — borax, washing soda and citric acid are harmful if swallowed and irritate eyes and skin. Keep silica packets away from kids. Homemade powders can etch glassware or void some dishwasher warranties; test first.