Now that I looked again, Im 95% sure its K def. My reasoning is because of the leaf edges are where the problem is focused, and the bronze color of the necrosis.
Foilar feed with nutes high in K until ur soil is on the dry side (to let the roots get a good breath of air before the flush). Then flush them with about 5 gallons of water with a light nute mix PH of 6.5 and finish with 1/2 gallon of regular strength nutes PH 6. Make sure u are using a good nute mix for cannabis, this will take some research and make sure ur PH is straight and ur problem will be solved. I use General Hydroponics Flora Series Micro and Bloom for vegging and blooming. For vegging u can use 5ml of Micro and 10ml of Bloom per gal of water and u will have a sufficient nute package for the roots to feast well. Then for flowering use 8ml Micro and 16ml Bloom per gal. This is the simplest nute program in the world for cannabis. I suggest mastering something simple like that before u get into any complex programs.