The PM stays inside the plant tissue so yeh it's sort of always there, that's why you want to remove as many of the leaves that had it as possible. I don't have any experience with citric acid but I guess you could? Oxidate is a peroxide product that also contains peroxyacetic acid. Purecrop1 is corn and soybean oil but it doesn't act like an oil, they change it on a molecular level somehow, so it doesn't cause burn like an oil typically would. It'll still burn the tops (the hairs) a little bit in bloom but the bottoms should be fine. Anyway those are the 2 products I use for knocking down PM. I use regalia too which is like a plant immunity booster.