[DURBANPOISON.AAA]

So, initially I thought this might be a bit of light stress so I reduced the light intensity however it did not seem to help that much. I am currently growing in coco/perlite & using liquid nutrients.
I am planning on flipping to flower soon so I was going hard on the nutes. Any advice on what could have caused this & how to fix before I flip?

 

[ArtfulCodger]

Tip burn, running down the edges, and dark leaf color in general. My vote is over-feeding. I'd back off the EC.

 

[BrucieBuds]

Light stress I think imo bottom leaves look healthy so not nute burn that would effect everything

 

[Ninjadogma]

What are you using for feeding? Looks happy with it whatever you're using. Technically what you likely have is a light related nutrient deficiency. The outer edges are radiation burns and the lightening of the pleats on the top leaves are developing magnesium deficiency because it's being stripped away by intense light radiation.

For a plant that age I'd suggest raising the light or dimming it down if it has that feature. The documentation for your light should tell you what distance and/or power setting will get you to 400.

Good luck with the rest of the grow, and keep us posted on the plant's progress!