Any ideas on what this could be? I checked the PH and it is right around 6.5. I did feed them twice last week as I was out of town over the weekend. When I got back the temp in the tent was °91. It's bad on one plant and starting on another. The rest look healthy.
Here's an image.
https://dutch-passion.com/img/cms/Blogs/Boron-deficiency.jpg
Though boron deficiency can also look like yellowing, curling, weird growth, etc.
Probably got a little heat stroke from the temps but they will be fine if you got everything back into parameters upon returning and they seem happy. It’s a slight toxicity from it having to over perspire during the hot period. The only water it could use was from the soil. Uptakes a lot of water/food. Stoma closes because it is richer cause it’s drinking faster than it would. Very vicious cycle if left unchecked. Glad you caught it and happy growing!!!