Gelato #33 "The Larry Bird Cut"

The highlight of this week is whatever the F is going on with one of my plants. The back right plant has developed scrunched up leaves that have dark patches. The conditions are all the same in each bucket, 6.2 pH and same nutrients and the other two plants are looking very healthy. More recently, the scrunched up leaves began to get dry and crispy. Does anyone have an idea of what's happening? Someone I asked had said it might be a nutrient issue. I just refilled each plant's bucket with 4 gallons of fresh water and nutrients yesterday.