OG kush starting to get dry leaves and falling off?

She's 3 week into flowering and she just got fed water with just 5ML of Calmag .
What could it be?

Could I ask bit more information? How far are lights from the plants? What feed you give em? Whats the PH level and whats the humidity?
I have my first grow currently in going and I had the same problem, I raised the lights about 10-15 inches from the tallest plants and got my humidity up to 30-50% and now the problem is solving itself.

if you put your hand over the top of the plant, is it hot? could be a temp issue.

Signs of overwatering. Got any other nutes besides cal/mag? She needs bloom nutes