Bizzare Plant Sickness...

Ok, so here's the quick version:

I'm growing hydro (DWC). I have a reservoir with 3 plants in it, so they all get the same inputs (light, air temp, pH, water temp, nute levels, DO, etc.)

In the beginning of my project, I neglected the plants for a little over a week, so they got sick. However, I've been nursing them back to health. But, while 2 of the plants are growing pretty well/getting better, the other looks really terrible. Since they've all been getting the same treatment, the only thing I can think of is that the person who gave me the clones accidentally gave me 1 clone of a different strain, and it's reacting differently because of the genetics (they are all supposed to be Big Bud). But, then again, it could just be a problem I'm unfamiliar with.

I've attached some pictures. 5-24(1) and 5-24(3) are the plants that are doing well/ getting better. They are clearly a bit sick, but nothing critical. However, as you can see in the other two pictures (5-24 before/after pruning), the third plant is in really bad shape.

Let me know what you guys think.

P.S. If you need more background, check out the link to my grow journal (it's in my signature).

Update:

So, I realized that I had accidentally been using the wrong nutrient ratios, so there was just a classic nutrient defiency. As well, I used Advanced Nutrients Revive. After a couple of weeks, my plant's look MUCH better; here are some photos

yeah dude, see the yellow leaves with the green veins? thats mag deficiency

thanks for the info, makes sense (+rep). revive basically has several nutrients, calcium and magnesium among them. My plants are much better, but one of them still has strange spots on teh edge of the leaves...but only 1 of them...

see the spots? is this still a mag issue?