Heat stress, ph or nutes, you be the judge

I have the nutes at 1.5 EC at the moment, I have been careful to keep them below 1.8 as there seemed to be some burn taking place in my spray hydro setup.

Ph is currently 6.6 but I allow it to fluctuate between 6.6 and 7. Temp is 28 Hum is 60 ish at the moment. and sticks to around there.

The problem could be heat stress or some moisture that was on the leaves from me trying to up the humidity by spraying water over the foliage. I have added some pics as it almost looks like a bug has been eating a layer of the leaf. I have checked with a magnifying glass and can't see anything.

It is worth noting that there isn't much going wrong on the grow but I'm keen to fix things before they get too bad.

your plant looks strong. I almost want to say that it's a calcium deficiency, but that would really be all over the plant. if it's just in one spot, it looks like you might have burned the plant by letting water hit that spot and then letting a strong light magnify it's way through the water to the leaf. I've had this same problem before and as long as it doesn't spread, you're good.