How hot is it in ur tent? How far away are the lights? Your plant is clawing down, seems like heat/light stress, lack of water/ or too much water. How often are u watring?
Your plants look green, dunno about the lack of nutrient. If you spotted an insect like a thrip, you should check ur stems and under flowers before sunrise/sunset. Get some sticky traps and put them in the pot. Grab some Damascus earth, sprinkle it in the soil and on the tent floor around the bottom of the pots. Try to identify/grab a photo of the insect.
Thrips can cause those brown rust spots. I don't think its a deficiency. Try NOT to use neem oil its not good for the buds. Did the insect look like one of these?