Im sure it's the lack of humidity now....I have my fan slightly too close to one plant in my room...(she's saving the rest from the same fate.) She has leaves on her that look exactly like that. I tried to upload some pics...but I have to resize them....if and when i upload....keep in mind that im 9 days from harvest, so the lower fan leaves have yellowed from lack of nitrogen and intense light...my fan is aimed low at the plants so i dont dry buds ...just wanna keep air moving...like I keep telling you, get a humidifier...your night time humidity is good...but im sure it takes a while to build up...check the humidity every 45 min or so after the light goes out to see wich way it goes, up or down, then act accordingly. I am almost POSITIVE that this is the problem....especialy when you say some leaves feel dry and crackly....and others dont...lemme guess...the drier feeling ones have spots etc? Overtranpiration my friend....leaves cant take in moisture as fast as it is expelled in a dry enviroment...makes sence doen't it?