Ok I might be a noob who has no idea and it may be a nitrogen deficiency, however, how can anyone know it is a nitrogen deficiency without knowing what nutes you are using. The pics tell more than one story! If you are using nutes, then my money is still on over-nuting. If you are controlling your nutes well, then yeh it may well be a nitrodeficiency... do you have air pump for reservoir?Yeah its a combination of the following. These noobs have no idea. The main piece of evidence is the yellowing of the leaves from the bottom to the top. I'd say give them some nitrogen fert and cut away dead and yellow leaves. As for the plant on the right top it to keep it away from light.
either this guy has the lower syndrome or hes trying to fuck with your grow.. if that was a deficency your leaves would be yellow at the bottom and not burned. if anything you fed it way way too much. try flushing it out and removing some of the dead leaves. (those brown leaves wouldnt be there unless they have been yellow for weeks and then died) ive brought back overfed plants but it took a while to see improvements. if you keep records of your feedings look back and see if you started with a full strenght mixture or just fed it too often.The plants are two close to lights on top that whats causing the dead leaves on top of the right one. Also maybe lack of air flow going on?
There is also some kind of def. going on in your plants. To the best of my knowledge i would say lack of nitrogen, Have you been using any fert.?