Hey RabaneteBrasil, how's it going? Welcome! I’ve had the same problem, and it’s really annoying to fix. Check out my NL diary to get an idea of how I progressed. The important thing is not to remove the affected leaves; despite their appearance, I got the best results in terms of yield. No doubt you’re having issues with mineral absorption; I see calcium and magnesium as others have mentioned, but to diagnose correctly, I’d like to suggest a few measures and give you some tips to avoid this. I’d like to suggest: A / RUNOFF - take a look at the pH of the runoff; if it’s too acidic and PPM or EC is high, there are salts present in the substrate causing the problem or overfert. If you don’t have a meter, there are simple strips sold in grow shops that are pretty cheap, and it’s important to regulate the pH of all waterings to around 6.5. B / One tip I can give you, if you have access, is to use a product with beneficial bacteria and mycorrhizae. I use Recharge, which has various types, and I highly recommend it. It’s really worth checking out and testing; it basically prevents this type of absorption problem and roots better, along with pH and nutrient lockouts. C / Another maneuver I would try if you do the tests I mentioned in point A and it’s positive would be a flush, and finally, I would give a calcium and magnesium supplement, as correctly mentioned, beforehand. D / Also, take a look at your watering practices; wait for the substrate to be dry by testing with your finger up to the second knuckle and feeling the weight of the pot to avoid excess or deficiency. Fabric pots help a lot in this regard and speed up plant growth. 15L works very well for autos. I hope it works out, and if you need anything, I’m here. Cheers and good luck with everything!