I had a calcium look out (maybe the soil got to dry on me) or calcium deffiency and one of my plants leaves got some real nice rust spots. I'll say I want my plants to look great but also want them to grow I probably do feed feed water and if I see a little nute burn on the tip switch to water feed water feed. I personally use urb when I water and added some unsulfered molasses for the calcium in it. My issue with the look out was early week 4, I'm finishing week 5 and the dead area are still dead but the buds growing nicely. Best of luck. Pics for reference first is before second after.