phuckin horrific downward curling yellow leaves of death creepin up my plant

Its illedgidly skunk#3 I've followed the foxfarm tri pack schedule preety close, and a lil super thrive once a month. My darktime temps really drop but 50 was the min, batteries died in my Ph tester so I couldn't say about that idk even know if the damn thing worked anyway.ill post a pic when my lights come on but a friend convinced me to clip the yellow off so it might be hard to tell.Attachment 281042 this is it a coupla weeks ago. But its getting worse and headed tward the bud sites. Also I know they need their dry periods but how dry and how long.