Ph fluctuations
That was my first guess, I’m no pro. Though!
Looks like, here you’ve got more info … 
Better safe than sorry 
Ph is exponential, so a full point of fluctuation is alot. I always try to adjust it over the course of say a week if it’s way high
Everything starts to go wrong when the PH is off check every time you water or feed
And @Esrgood4u also would say: check and calibrate your pH measurer or you could have serious problems … 
That fuggin Ph… always likes to f with people
Yeah don’t freestyle that thing like I do. 
Hahaha “J ‘imma freestyle everything’ Bug”
Thank you my good man. I’ll probably get a gallon of water ph it, then just use that gallon the last of the week instead of ph a bottle of water every time I feed.
The fertilizer can throw off the PH levels best to check after you add fertilizer
Example my tap water plus 500 ppm of jacks puts the water ph at 6.3 sweet spot
no fertilizer add my tap water is 7.5 ph
It all depends on your tap and what you use
I’d do a little run-off test first and foremost to check pH and PPM…
Also looks like you might have a possible Thrip problem starting(possible damage on background plants)
Alaskagrown
How can you tell if it’s thrips man?
I don’t see the greasy looking residue here from thrips. Their larva are like tiny slugs.
I agree with the others above about ph problems.
I have to check after adding nutes, and then I wait a while and check again before doing the water…
Looks like a variegated leaf to me 
But idk I’m way past my bedtime and I’ve been smoking that jungle shit again 
Thought this could be Thrip damage…but don’t see any poop…probably just the same issue happening on another plant.
Alaskagrown
Yes 100% do this. You can very easily loose your entire grow if you don’t. 
You been stealing my tap water? That’s my situation right there. 7.x out the tap, add my Jack’s and I’m at 6.3-6.4. add my cal mag and I’m chilling in coco range 5.8-6
We be the same lol
Are you on the east coast?