Yellowing after 3 weeks flower is it Nitrogen Deficiency ?

[grinn3rz]

I am growing in a 2x2m tent with 4x400w cooltubes , using perlite in pots  , have been flowering for 3 1/2 weeks now and yellowing is spreading up fast on 2 out of the 10 plants . to me it looks like a nitrogen defiency but I am not 100% sure . the yellowing started down the bottom shade leaves about 4 days and is spreading up like wildfire , today the buds are starting to die of as well . anybody have any Ideas on a quick fix for them ??  strain name is unknown I took cuttings of a friends plant , I am using Cyco nutes with potash , sugar rush and zyme . ppm is at 1100 at the moment . ph is 5.5 .

[Stix87]

hey i would rise my ph up seems a bit low

[Ozzy420]

IMO they are fine, the dieing off it part of the plants life cycle, drops what it dosent need any more...

[ZEN2U]

I have seen something like this before, the problem then was mites, don't know if you have the same problem.

 

Until I read that the heads were going the same way, I could of assumed that it was a natural process of the plant withdrawing all sugars and nutes from the un-needed large leaves for reuse in the buds. I think this is what Ozzy has suggested.