Strange shape on leaves, Edges pointing up.

Hey guys!
This is an old picture.
I have seen this phenomenon in almost every grow i've done, except for outdoor grows.

I've searched internet but the only answers i found was regarding heat-stress (wich is not the cause in this case as i'm very specific about checking temps!) im seeing similar shaped leaves now and my temps are at 21c (70 farenheit)

My guess is overtfertilizing or ph-issues?? Anyone knows?

Thanks!

How's the humidity?

hey
I keep it between 70 - 80% in veg, and 60 - 70% in flower (flowering humidity depends on strain)
Thanks for checking in!

I just saw a thread were a person gave his plants water with an EC of 1.8 and his leaves were similar, but more extreme. So im guessing toxicity? wht do you think?

This picture is taken of 2 hindu kushes grown in soil an ok smoke now after cure, but could've been a better grow with some bending-techniques.