Hey, how's it going? I'd also guess it's a deficiency. Maybe phosphorus or potassium. You can easily recognize a deficiency when the lower leaves burn or dry out. In the case of nutrient burn, it's the upper leaves where the tips burn and curl up a bit.
Increase the PK ratio a bit or split your feeding to 50-70% and do it twice a week. This way, the plants have a continuous and more regular supply of nutrients.