All the bottom leaves are dying

All the bottom leaves are dying and falling off, they are going really dark brown/ black.
A few leaves on top have a deficiency, not that many. Can anyone help me on what it is and what to do.

I'm on week 5 of flower
growing in coco
I feed them once a day
Ec 1.2
Ph 6.2

it looks like its not getting enough light have you loolipopped it yet? thats when u trim the whole bottom of the plant because they get no light so they r pointless to grow