Have you seen white spots on your leaves? Are your leaves dusted with round patches of powder that looks like flour?
Example of white powdery mildew (WPM) on a cannabis leaf
If so, you’re most likely dealing with White Powdery Mildew. Mix up your treatment of choice in a clean sprayer/mister. I recommend Lost Coast Plant Therapy (1oz/2btsp per gallon of water) or GrowSafe (2oz/4tbsp per gallon of water) as a safe second option. Make sure to consult the instructions on your treatment of choice to find the recommended dosage. Wait until just before your lights for off for the day and mist your (newly cleaned) plants. Get all the leaves even if you don’t see WPM on them!