Two days ago I sprayed some magnesium because I noticed what looked like a mild magnesium deficiency. I also added some Botanigard to the mix, as some of the leaves looked a little fluffy, which I assumed was from low/no humidity (i'm in the mojave desert), but just in case I wanted to maybe hit some mites if they were the culprits. I glassed and didn't see any, but you never know, you can miss them. Yesterday one plant started to show signs of the leaves curling up, not tacoing more like burritoing. So I dropped the temps, sprayed a little more, and tried to increase the airflow. Today I woke up and the one plant that is in the picture three was basically dead and all my plants were showing symptoms. I have no idea what it is. There are some light blackish areas in the most advanced leaves that isn't like spotting, but just like necrotic zones spreading. And than like mid level advancement kind of look like how mildew is being described here:


But I don't know for sure, because clearly the most obvious symptom is the leaves curling. What do you guys think?