Nutrient burn or light stress?

I’ve noticed the tips of my leaves are starting to yellow.
Is this always a nutrient issue or could it be light/heat stress.
the plants had stretched a bit and tops were only a foot or so from 600w HPS.
EC is 1.4. PH5.9




cheers

I'd suspect heat.


What's that flashlight looking thingy hanging up?

Slight nitrogen excess. Consider reducing your nitrogen a bit.

You’ve got some heat stress going on. Separate issue from the blanched tips.

Cheers. I thought it might be heat but will watch the nitrogen too.
The orange flashlight thing is my temperature and humidity sensor, (ibebot, Air Comfort). Looks a bit weird but does the job lol