Pretty classic Ca issue. My best guess, looking at the dark green color of the leaves, is that a bit too much N is locking out Calcium. Ease off on N, and keep up the calcium. If you’re not feeding N, up the Ca anyway! The other option is to give it a good flush, reset the soil and go back to feeding and calmag. (Reduced N). This is for soil, it would also be helpful to know what your media is, your nutes, feeding schedule, and ph of nute water.
Technically it's manganese toxicity. I never understood how the Cannabis community has missed this, since I started growing in 74 and learning cannabis nutrition was not an optional task, it was the sole route to financial success over the following 2 decades.
Shortly after beginning my growing career I moved to an area with high Mn in the soil and everything went orange. We had the leaves tested and they had toxic levels of Mn, in the hundreds close to 1000ppm on some varietals. Cannabis cannot tolerate the Mn it accumulates. It needs maybe 25ppm. 40 at most. Cannabis is a hyper accumulator of Mn and I've had countess fights with weeds nute lords who insist on using trace mineral profiles for tomato and selling the extra bottle to counteract it:
My consultant at the time told me to use high amounts of dolomite lime to restrict Mn uptake. I added so much limestone that I locked out pk and also hermed the crop. And at that point I decided to become my own consultant. Nutrient balance is the only factor that mattered in our grows. Everything else could be essentially ignored and the product would fetch full price. Ignore nutrient ratios and the quality slips drastically.
That's why weed was really good in the 80's. We figured that shit out on our own and it had to produce the best bud or you became the drought-only supplier sitting around waiting for everyone else to sell out before old friends would reluctantly call you up. Alot of the difference between today's weed and 20th century weed is simply the ratio of excess Mn to Mg and the way this redirects energy in the mevalonate and methyl erythrol phosphate pathways.
Light burn?
The effect of light intensity on antioxidants, antioxidant enzymes, and chlorophyll content was studied in common bean (Phaseolus vulgaris L.) exposed to excess Mn. Leaves of bean genotypes contrasting in Mn tolerance were exposed to two different ...
www.ncbi.nlm.nih.gov
Abstract. Background Manganese (Mn) is an essential micronutrient that is phytotoxic under certain edaphic and climatic conditions. Multiple edaphic factor
academic.oup.com
Calimag deficiency?
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pH issue?
Mn is the heavy metal that fucks up Cannabis worst. Worse than cadmium. Worse than lead. Yet, look at this soil recommendation for hemp:
20ppm Mn? What the hell??? The 0.8ppm already would kill a Cannabis crop in that soil.. Summon Calimag.. Calimag!! Cali Mag Shakti de!
Just thought I'd clarify why pot growers think lower leaf spots could be a immobile nutrient issue. Since the actual purpose of Calmag has kinda been lost on the scene: It's a bandaid for garbage quality relabeled high Mn low carbon high nitrogen tomato nutes.
