Random yellow leaves, help please

[Whitehotdog]

Can anyone diagnose this .
1 plant of 4 has random yellow leaves but rest of the plant and other plant are OK. All plants get same nutes .so strange why just one plant effected.
Looked close the blavk dots and they are not bugs on front or back of leaves
Thanks in advance

 

[RichieRich6988]

What cycle are you in? Because if you are well in to flowering cycle the larger water leaves will do that. Also if you are not using any Cal-Mag I would strongly suggest it.

 

[MochaBud]

If you were in soil, I'd say a "P" def caused by a cold root zone....mine do that when my floor temps are below 68F

 

[Whitehotdog]

Hi
Thanks for quick response guys
Sorry I should have given more details
It's in coco and still in veg ,I'm using gh nutes and cal mag .
But mocabud could be onto something the plant in question is nearest the air inlet. So would be the plant getting the cold air blown onto it more than the rest. If the same applies in coco. But I'm just clutching at straws to be honest .