Can't work out if I need to worry??

Hi guys,
I have a problem with one of my girls at the mo. Problem started 2 weeks Ago. I'm not what you would call a noob, however have been really lucky when it has come to problems/ deficiencies. So have limited experience correcting issues. I basically have yellowing of some leaves. Mainly older, however some new growth seems to be Going more pale. I have some brown spots in places. It's worth mentioning I did have a couple of big stem breaks whilst training so I'm wondering if it was shocked and this is what caused the older leaves to be damaged.
I run canna full nutrient line checking ph and run off frequently. All is normal.
In the pics below I've added a pic of a leaf that's fairly new growth compared to the badly damaged leaves. It seems since the symptoms came to light, growth has slowed also.
The strain is moxie seeds: alpine og.
Anyone's thoughts on how it's looking or any idea on the cause of this to the plant would be appreciated.
The pics below were taken just after some training so that's why they look uneven in places.
Cheers.

Set up: 600 wat hps
1.2 m grow tent
6 inch carbon filter/ fan
5 inch inline
Air cooled reflector
Fans
Humidifier

Humidity: 55-60
Temp 20-25 c
Ph: 6.5

big stem breaks dont shock vegging plants. I've hit them with a lawn mower outdoors and they grow up proud again if they have time

I'm literally clutching at straws. It's not the conditions or the ph? It's some sort of deficiency. My other girls are doing fine.

I have had stunted growth from stem breaks before. nothing like this so I know your right.