Brown spots?? Calcium???

I had a look at your diary. I also had a look at your nutrient you are using. All the elements are there including calcium and magnesium. It looks like an organic fertilizer derived from bone meal and other natural sources. It says it's readily available to the plant and is also slow release. Personally i wouldn't use that kind of fertilizer without Mycorrhizal fungi and beneficial bacteria along side. Weed is very demanding for nutrients and consumes a lot. And nothing says it uses nutrients evenly. Some elements deplete faster than others. I don't know the back story of that nutrient and what it's marketed to be used for but it's not likely formulated to be used to grow weed. If it's only displaying near the top of your plant and the bottom is ok then you know it's a immobile nutrient thats the issue. That at least narrows it down. In the future i wouldn't use that nutrient. I would grab yourself some nutrients that are marketed towards growing weed. Reduce your pH to 6.2. Calcium is best absorbed at that pH. If you wanna stay organic then grind up some egg shells in a food processor or just pulverize some into powder and sprinkle it on your soil and water it in.