HELP! Yellowing leaves

[Redtomato]

My greenhouse grown OG Kush (feminised, photoperiod) has grown like a weed (!) but over the last couple of weeks some of the leaves have started yellowing.
There doesn’t seem to be any pattern to the yellowing - photos attached
I appreciate it could be a number of things - over watering, irregular watering, temperature changes, insufficient nutrients, too many nutrients, root pH, but I’d welcome the forum’s opinions
Please be nice, this is only my second year growing!
It’s being in grown multi purpose compost, in an air pot.
I’m feeding it with a general purpose feed

 

[TOKABIGONE]

Good morning Redtomato were all nice here....usually. Nice looking little tree. As the plant ages they will start using nutrients from the bottom shaded fan leaves to fuel new growth and flowering. Yours are just beginning the process.

 

[Redtomato]

Thank you TOKABIGONE! Is that still the case with random, different size leaves elsewhere on the plant?

 

[CaptainWiese91]

Nothing to worry about ! Really nice looking plant. Second grow - that is really good 👍🏻
Good job

 

[TOKABIGONE]

As long as it's not in the new growth it's pretty normal

 

[PLreef]

She looks pretty good over all. I'd add a little cal/mag to her diet. What is the NPK value of your all purpose feed?

 

[Redtomato]

Thanks PLreef
It’s 4-3-8