Powdery mildew ??

If it rubs off the leaves and is not sticky its likey WPM. If its sticky its likely trichomes. You need to remove all the leaves affected and increase the air flow and decrees the RH should it be WPM. If you can not decrease the RH try defoliating some of the plant for better air flow, keeps the fans on. Milk is not very effective in my experience. potassium carbonate is a bit better. altering PH is the main goal. Once the fungus is showing it means it is in the structure of the plants leaves and they need to be removed. you can control it slightly till harvest but it is everywhere. Best to bleach or peroxide the tent and its equipment after this grow. if you can't control the infestation trying moving it outdoors UV can help kill off WPM. for future grows find some Silicon for the plants as this can help make it harder for the fungus to establish itself on the leaves in the first place, thus preventing it from growing and becoming an issues. Wet leaves at night time and overly wet soil can help this fungus spread. watch your dew point. Good Luck!