Someone is really thinking about this! Keep it up! The EC is fine... I also have 0.7 in the Munich water by default (when the farmers are still farming). With good ventilation (and it looks like that!) it doesn't matter as much with over-fertilization. I even go up to 2.0 and more at the end.
Your night temperature is too low. With DWC or aeroponics, I wouldn't go below 20 degrees. Also, the nutrient solution should be between 20 and 21 degrees. If your temperature drops that much at night, the air can't hold the moisture anymore, and it settles on your leaves, which is why you're getting mildew. Get yourself some purolyt. It's good for everything, including the roots. Good luck!
@Gnrlymsntrp81,
Hey, thanks a lot for your reply! With the extreme temperature changes, I feel like I'm really falling behind. This is my first grow in this location.
It's completely new to me that a too low temperature causes problems. Even after 12 years for sure.
I've now defoliated a lot, especially the affected ones (early stage) since I still need to order purolyt. I will now clean thoroughly and counteract a bit with H2O2. I'm already using a heater that absolutely can't be regulated with a timer.. and 1x 100, 1x 125 intake + 350mm exhaust fan + 3 fans. It must be due to cleanliness or much more likely the temperature, right?