Please help us identify the deficiency going on wi...

looks a lot like the pH issue I had with my peyote critical. Wrong pH will replicate lockout as the roots won't take the right nutrients in and it starts to starve of the deficient nutrient. check you pH first as that's the easiest thing to fix. I found I needed to lower my pH so I added a little lemon juice to my water to make it more acidic as a natural pH down. I used 0.45ml to 2L of water. obviously your base pH will differ on your volumes needed for whatever you need to add up or down. hope it helps and best of luck with the best of the grow?

It looks like a magnesium deficiency to me. A magnesium deficiency shows up first around the edges and in between the veins on the leaves. The first leaves to show these signs will be the oldest ones, and the ones closest to the bottom of the plant (often, these are the same ones). This is caused by the plant withdrawing magnesium from these leaves in order to send it to the newer ones, in an effort to keep itself alive. In non-soil and hydro systems, the pH should be 6.0 – 6.5 for the best magnesium uptake.