Sounds like white powdery mildew.. i looked up the best way to treat it is to use distilled water and wipe it off each leaf. You can use a solution of 1 tbsp baking soda, 1/2 tsp liquid soap in 1 gal of water and spray on leaves to control the mildew after you have wiped it away. I wouldnt use that solution if they have buds on em. What is the rh in your tent? Is there enough air movement?
I have heard you can hit the plants with silica in a foliar spray and its supposed to be good for helping prevent PM. Its recommended in gardening of cucumbers and squashes that are very susceptible to PM. Might be worth spraying and giving it a try. Not to mention silica as a spray helps with pests as well. I plan on incorporating into my routine.