Dry brittle leaves

This looks a lot like your oldest grow question. growdiaries.com/grow-questions/36908-noob-grower I would say it looks to me that it was burned by something. maybe water on the leaves or PH issue in the soil. If you watering at 6.5 whats your runoff measuring at? Would not be surprised if this is a salt related thing as well that will be detected by monitoring your EC/PPM of feed going in and runoff coming out. Let us know the numbers to better help you. DM me as we won't get notifications of when you reply to this questions page. your inbox is that little green arrow on the bottom right side of the screen. Good Luck!

This could have some underwatering if you believe it’s not overwatering. But besides that It looks like phosphorus deficiency to me.. which can be from having your pH off as well.. phosphorus has a tight window, if you’re too low (below 6 or so in soil) it will lock it out, if it’s too high (above 7 in soil ) it will lock it out. https://www.growweedeasy.com/wp-content/uploads/2010/05/soil-ph-chart-marijuana.jpg

@Misanthrope your humidity is fairly low mate which could be contributing to those dry leaves I am also concerned that the leaves are a very dark color perhaps a tad over done with the nitrogen however the lack of burnt tips means it should not be too much of a problem if the humidity is too low in the tent you can try hanging a wet towel in there which can help add some moisture to the air just trim those burnt leaves off and keep an eye on the RH