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Nute burn is generally right at the tips of the leaves.
I would generally associate yellow in the middle of the leaves like that with pH. I had a bit of something similar to that at the start of my grow this time, I think mine was a bit of a combination of pH problem when they were young and I wasn't watering to runoff yet so I couldn't check the runoff pH to see what was going on at the root zone on top of a little heat stress as well.
Also 30 cm is the closest you should be with your light, you could try raising it to 35cm for a couple of days and see if it makes a difference