Preheat oven to 325 degrees. Grease a loaf pan and set aside.
Combine flour, baking powder, baking soda, and salt in a medium bowl. Set aside.
Beat butter and sugar in mixing bowl until well combined. Add eggs and beat in eggs until combined.
Add flour mixture and milk alternatively to mixing bowl. Mix until combined.
Add grapefruit zest and 1/4 cup grapefruit juice. Mix until combined.
Pour batter into greased loaf pan. Bake until top is golden brown and toothpick inserted in middle comes out clean, about 1 hour.
Allow bread to cool in pan for about 5 minutes. Then remove and set on a cooling rack.
Prepare glaze by combining powdered sugar and 3 tsp grapefruit juice. Stir until desired consistency. If glaze is too runny, add more sugar but no more than 3/4 cup
Pour glaze over bread. Serve and Enjoy :)