Your plants are looking good bud. The deficiency you have there looks similar to mine. I gave them plenty of water last night with calmag, but this morning they look a little worse. So maybe I have a potassium deficiency as you suggest and not a calcium deficiency as I thought.
Will feed them again tonight, and bump up the bloom portion a little to see if they respond well.
EDIT: I just had a look again at the deficiency chart and i definitely have a calcium deficiency. Maybe I'm being a little impatient.
Mine take a couple of days to recover when I give them the Cal/Mag for sure. I would say give it some time. ;-)