Plant deficiency. pls help!

[TokaCola]

I have 12 plants that are very light green and are showing deficiencies in the leaves. I'm thinking maybe nitrogen and magnesium. anyone have a solid idea on what it can be?
This is planted in COCO in dutch pots. I'm using COCO A & B for nutes at quarter strength with distilled water and alternating to just water every other watering cycle. Ph is 6 to 6.5. temperature of the cab is 71 degrees.
The plants are growing but the leaves are staying yellow. these are oaksterdam green cush (crack) strains. i have placed a healthy plant next to the sick plants. I hope someone can help me! here are the pics....

 

[Jalisco Kid]

If those are clones why are you feeding them 1/4 strength? JK

 

[Rootbound]

What is your runoff PH and EC???? RB

 

[KushMaster707]

looks like n deficiency my buddy started his green crack off at 500 ppm of calmag and sensi a&b and was able to bump em up to 700 ppm the next week

 

[TokaCola]

i started them at quarter strength cause i was told to so i avoid nute burn.

the way i have my drain setup, there is very little run off left in the drain to test.

should i bump the nutes up then? what can i add to fix a N def?

 

[Calimad]

i believe you need to ph to 5.8 for coco. 6.0 for youngsters. get that right and water with some N @ 1/4 strength . Hopefully that might work...