1/4 teaspoon of WHAT?
Your goal is to raise the pH. Jsut your tap water alone shoudl do that, since it is significantly higher. But if you have plant pH up/down, make a solution at 6.9 and flush with that until the runoff reads 6.7. Use 3 times the water as the volume of the pot. So basically, make 3 party cups worht of water at the right pH and use all of that. Then you should be in much better shape.