Plants suck up all the N available to them resulting in dark green leaves. Thus if you see dark green leaves with brown tips, there is a good chance you are dealing with nute burn. Back off on the nutes and see what happens. There is a purplish tint to your leaves. That could be natural to your variety or indicative of a lack of P. That is what you expect if you are using vegging nutes (lots of N, not enough PK) in flowering. It could be the lights though. It's difficult to see the true colors under HPS or LED colored lights.