This is already my 3rd grow so I've got some experience in same cases but not all of them.
Grow Info:
Light: 400W HPS - Philiphs Son-T Agro
20" fan
10l pots
4x Short Ryder Autoflowering
L = 1M, W = 60cm, H = 1,5m
I've made some research and from what I've read, it might be an Iron deficiency...