Leaves curling upwards and dieing...

3 Weeks later...My biggest problem was I was using reused potting soil. Saying that my PH drain-off was at a low 4.3. I was able to flush and bring the PH back up to 5.75-6.00. They are looking soooo much better. I am keeping a close watch on everything now. They are at 9 wks veg. On 18 hr light. If all goes well I'll get 4 harvests out of this soil. Next planting I won't be so cheap. Smiles.

When the serrated edges of marijuana leaves curls or tipped up like that, it’s often a sign of temperature stress, overwatering/root problems or extreme humidity levels

Thank you, both. Very good advice and also helpful. I can fix this problem now. Smiles

Looks like severe N burn and possibly extreme heat stress. You need to test your runoff. If you don't have an EC meter, then test the pH of runoff. I would be willing to bet you're in the high 4s or low 5s. If I'm correct, flush. Flush and flush again until the runoff comes up to 6.3-6.5 (btw that +/- 0.2 is actually a large margin of error). Use 7.0-7.5 water to flush. Get an EC meter, learn how to use it, and use the data you gather to determine how much or how little to feed. The germination page of my GDP diary has a full equipment list. I went for the cheapest, but fully functional, equipment. My diary also focuses pretty heavy on EC readings so you may learn everything you need to there. I do hydro and it's way more important for hydro, but the general idea is still the same. If the EC of your runoff is higher than the feed, then feed less. If the EC of runoff is lower, then feed heavier. Hope this helps. It could also be heat in excess of 90°F and it could be a very poorly calibrated pH Meter giving you bad readings.

I believe you have a Broad Mite infestation.