Just have to keep doing these PWC until it's below 0.25. Do another 50% tonight and test in the morning. Make sure when you compare the test tube to the chart, look at the tube in a very well lit room, or against a window. Sometimes when you have the tube against a darker surface, the solution in the tube will look a bit darker and make you think you have some ammonia. Not saying you don't have ammonia, but make sure you check the test tube in a very bright light.