Maybe I'm not reading it correctly but do you have a week or a month left? Thought you said a month in the beginning and a week at the end. The problem with PM is when you see a little bit of it, it's already everywhere and that leaf is covered. I'm sure your going to have it on all your plants soon so I would spray with greencure or some other potassium bicarbonate product, I doubt you will get rid of it completely but that will at least help control it. If you put tarps around a gazebo did you put any fans in there? Fo future grows, air movement is a great way to help prevent it and spraying with a treatment or using a sulfur burner before you get it and at the beginning of flower is the best thing.