Blue Dream first DWC

Day 36-42 All in all proceeding nicely. Definitely the fastest growing and already biggest auto I have grown. Her Roots have completely busted the mesh basket and build a nice root ball. A small problem is her being such a powerhouse. Drinking ~2L of nutrient solution every day, she is massively increasing the humidity and with no choice but increasing the fan to avoid 80% + humidities the temperature is dropping to roughly 21°C. The really big issue though, depicted by the last picture, is the clear evidence of some problem she is having. I mostly ignored it in the beginning, but it is starting to spread and really worrying me. Even with some research I couldn't find a clear answer to this, so i hope some of you can help me out here. Especially you, @SwissKush... (The leaf was one of the most affected) Thanks in advance!!