Wth is this

Went out of town for two days came home to this. Not sure what's going on. Watered before I left. PH was 6.8 all plants are in same soil same nutes same light etc all doing great save for this one. I looked it up but that's its very obtuse for a newbie. Was hoping someone can lend me some knowledge or wisdom

I usually just tell what I see. I'm going to post this so you can read more about it.


Note the calcium relationship.

More CalMag, not joking.