50% green - 50% yellow , same grow -tent -tank ?

[Smeg]

hi guys and gals
i've got a problem .ive got 12 of these plants in one 2m x 2m tent . i've just completed a very successful grow with same strain
i've been using GHE Flora 3 part and cal-mag , mixed fairly weak , i added PK13/14 about 2 tanks ago

50 % of them are going a bit yellow , im guessing its a cal-mag deficiency even thou i've been adding cal-mag right from the start.
there all feeding from the same tank , on the Autopots system , so i cant understand why only 50% look this way .

not sure what to do ... should i start hand watering the yellowing plants with more/ extra cal mag ? do you think it is cal mag deficiency?
thanks for any input ,advise and comments
Smeg

 

[Hushpuppy]

That doesn't look like calmag deficiency to me. I believe that is Nitrogen deficiency. You said you have been using the GH3part but mixed weak. I would say to bump up the 3parts by about 50% of what you have been using. Do you check your solution with a TDS meter to see what the ppm/EC is? They look to be abouit 3 weeks into flower so they are getting hungry as they have ramped up the nute use while you haven't.

I would say that you should be feeding them with an EC of at least 2.0(1000ppm) and as much as 2.4(1200ppm) during flowering(heavy feeding Indicas will like as much as 2.8(1400ppm). I usually don't ramp up my "grow" part of the nutes when going into flower but I use it sufficiently during veg and then carry it over into flower for the first 3-4weeks and cut it back each week until I cut it off at the 4th or 5th week.

Like the guy on the "scott's Lawn care" commercial says, "feed your lawn, feed it"

 

[Hushpuppy]

Here is a typical magnesium deficiency that I got a while back in my MK Ultra when I forgot to put calmag in my nute solution in hydro. If you look close at the "group picture" you can see the discoloring around the margins of some of the leaves. That is a mild mag def:

 

[Smeg]

yea your right there about 3 weeks into flower . my ppms have been about 700-800 .
i'm doing a fresh tank tomorrow , ill mix it to full strength
thanks

 

[WeedHopper]

Nitrogen Deff is what I see also.

 

[pcduck]

Yeah your ppm's are pretty low, give them a boost.

Are these all the same strain?