Pictures, what's my plant's problem

I'm growing two strains (2 plants, AK47 and Northern Lights) right now in my 2'x4'x7' tent. I'm on week two of flower, The Northern Lights is doing fine; the AK47 is doing crappy. They're on a common recirculating sump with bubble buckets. 3 buckets; 1 of the buckets is a control bucket that pumps back to the other two. For nutes, I'm using GH Flora Series with Rapid Start, Floralicious Plus, and CaliMagic at 75% of the suggested concentration. I started using CaliMagic about ten days ago trying to fix this problem but it doesn't seem to have any effect. I'm keeping pH between 5.7 and 6.2. Lighting is a 600W HPS about 18" from the top of the plants. Whatever changes will impact both plants.
I have no idea what this troubled AK47 plant is asking for. The Northern Lights plant is healthy. Any ideas?
The color is a little wonky from the light and flash but you can see what I'm talking about. in the pic

i take it your do RDWC ? if so what is the temps of the water, how is the root ball?

Temp of the water is high 60s°F. Yes, RDWC. Ball of roots look normal and it's growing normally but the leaves look bad. This is the second time around of this strain for me. It did the same thing the first time around... Could it be bad genetics?

Looks like you're beating them up with a fan. And they look hungry for N.

which position is that plant at in the RDWC?

sound like you're over ferting. you don't mention what ppm you're using, but it apparent that it's probably too high. The lower leaf with the brown spots looks like heat damage. You're light is probably too close. GH flora has much of what plants need. It appears your giving so much because you can, not because you should. And know what your ppm is.

Don't see it been lack of N from them pics, since tops are worse than bottoms.

600w of hps is enough to light a 4x4 so in a 2x4 I would imagine its excessive. Could be part of the problem.

Air movement: Two small fans, one at the bottom of the tent and one at the top. The plants barely move with the fans on so I don't think it's that.
RDWC: Both buckets are fed separately from the control bucket.
PPM: Start of the week immediately after water change the PPMs are at 1140 and it drops through the week. I've experimented and I found 100% of the GH suggested feed schedule too much and 50% too little, so I settled at 75%.
Light: I'll try moving the light up a bit. Currently, I keep it at 18", give or take, but I'll raise it to 24".

Clearly I'm a new grower and so far. I've grown bubblegum, Sour Diesel, Northern Lights, and AK47... the AK47 is the only strain that has given me trouble. The only reason I'm growing it again is to try to figure out what went wrong the first time but I'm failing it again.

The need for Phosphorus is increased in the Flowering Stage.
http://www.ilovegrowingmarijuana.com/marijuana-nutrient-deficiency-phosphorus/

I run GH trio and FL Plus in DWC and max out at about 700 ppm with a 600 watt light, you might consider playing with lower ppm rates on your next grow. I've also had good success adding Hydroguard to the mix to keep the rez healthy.

I think you were right about the calimagic but it wont repair the old growth so you need to watch the new growth to see if the problem continues. I would also recommend the hydrogaurd product. I think your ppm's are up there too like above post stated but I dont see the burnt tips like you normally would. You made it this far and in flower so I wouldnt be to dramatic with changes but maybe drop ppms a little and definitely add the hydrogaurd. ............Whatever changes will impact both plants. Thats why I dont run different strains in a system but to fix this you can foliar feed or just top feed the problem plants...in veg mostly

I don't know if raising the light 6 inches will be enough.
I suspect that your using to many ferts for too long. I suspect the flora series is designed to be used by itself, although the company and others, make products saying there are good things for plants but you've got to wonder is that true or are they just after my money?