Yellowing leaves, crisping and dying? *PICS*

My plants leaves are going yellow and crisping to brown at the tips and dying?

Is it some sort of nutrient burn?

Ive heard about flushing but dont know really how to flush?

Could any1 help me and tell me what the problem is and how i can resolve it?

Thanks for your help.

Plant is in its 5th week of flowering.

To me it doesn't look like nute burn as the leaves are yellow all over instead of green with burnt tips but I don't know how long those leaves have been like that. there are so many factor.

Are you giving enough Sulfur? Iron? Molybdenum?

Depending on strain yellowing of the leaves in 5th week flower may be normal.

How warm does it get in the room they grow in? How far are the lights from the plants?

It looks like classic later stage flowering nitrogen deficiency but the browning looks like possible heat stress.