Noticed this leaf this morning, plants are just finishing week 4 flower and over all look very healthy despite two leaves that look like this. Plants a grown in Promix HP and are on a feed-water-feed schedule with a ph range of 6.2-6.5 when I water and feed. Pots get fully dried before I water. Temps, humidity and lights are all within normal ranges. I have been following my nutrient schedule and only thing I have added was bud candy with each feed. I do not think I have given any cal mag to this plant, but I use tap water, so I assume there would have been enough already.