Nodes turning yellow

Hey buds

Just worried that my nodes are turning yellow - i am thinking it could be a iron deficiency ?

But just want to check that its not something else .

I am growing in fox farm soil and under 600 watt hps . My room temp is at around 27 deg during the day and 21 at night.
My humidty is at around 55-60.

I flipped them to flower a week ago

Thanks
 

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