In week 4 of flowering using a coco soilless mix in 5 gal pots. Humidity is around 45%. 40-50% consistently I'd say. PH of 5.9 using Botanicare products. Flush at each change in 30gal reservoir- almost every week. So around week 3 (could have been earlier) I noticed some of the fan leaves getting a little dried out in random areas of the plants. More in the middle and top fan leaves, but not all. The bottom fan leaves are nice and green with no signs of normal dying off. Now in week four and those fan leaves started turning brown and crisp with some yellow/brown spotting. The rest of the fan leaves look good in the same area- green and starting to form the white frost on the leaves. Normally I would think nute burn if the tip of the leaves start changing colors but no signs of this. I checked for spider mites and other pests but don't see any signs from pictures I've seen online. The temp is around 78. In July it was pretty hot so it did get up to the low 80's at times. I've grown a few times but nowhere near an expert and I've never seen this. Any ideas? Thank you,