What is going on with my leaves ?

Ok, after having a good look, I'm going to say that it's not a Mag deficiency. Purple stems or dark veins in cannabis usually indicate magnesium deficiency, though this can vary by strain, very occasionally.. Leaf Necrosis from Advanced magnesium deficiency may cause the edges of older leaves to become crispy or exhibit leaf necrosis (leaf death), not seen here, yet. However, as the rest of the plant is looking relatively healthy, I'm convinced it is not an advanced magnesium deficiency. So what is causing this? Let's strip it back. If it is a Cal/ mag issue, this is easily remedied with a topdressing of dolomite lime. This will give your plants all the Cal/Mag they require, plus sweeten the pH and add trace elements and micronutrients, building a strong plant systemically. This couldn't hurt either way, as it's great stuff. I'm unsure what ventilation you have, but if you don't have extraction, humidity could be an issue. It is also possible that the pitting is done by insects, which can be fixed with a teaspoon of hydrogen peroxide and a teaspoon of apple cider vinegar per litre of water sprayed. I'm actually leaning more toward a pH or Calcium issue, which luckily, BOTH will be sorted by the top dressing of Dolomite Lime. It's not a cure-all, but it fixes many issues quickly whilst maintaining a balanced PH, you can keep building on. And in this convoluted market of a thousand confusing brands, Dolomite is cheap and most effective. Feel free to check my uploads to see how plants treated with Dolomite Lime grow compared to those with Diabolical chemical feeding regimes. There really isn't a comparison, imo. I also use oatmeal (and a bunch of other natural old school alternatives to keep the soil living) for added Nitrogen and Cal/Mag...also great fodder for the worms I've added to the soil to have something for them to turn into fresh castings in situ while the grow is happening. Don't fall for all the flashy brands; you will struggle to get the kind of growth and flavour achieved with a well-planned living soil. Your plant is not too far gone to remedy, and if it were me, my first stop would be Dolomite Lime topdressing, followed by seaweed liquid foliar feed. Then I'd wait and see for a week while just adding water. Hope it helps.

HandsomeTerpz said brown/rusty spots on older leaves are typical signs magnesium deficiency that is WRONG the old fans showing the deficiency of P (BROWN spots AND purple petioles, dark green color) right now that is FIXED also i notieced that old fans showed the Mg excess and Ca (look at the clawing tips ) lock, BUT that is history now

Based on the pictures, your cannabis plant clearly shows magnesium deficiency the yellowing between the veins and brown/rusty spots on older leaves are typical signs. Magnesium is mobile, so the plant takes it from older leaves to support new growth, which is why the issue shows there first. Typical signs you see here: Interveinal yellowing (veins stay green at first). Rusty/brown spots in the yellow areas. Starts on older fan leaves and moves upward if not corrected. What you can do: Check pH! In soil aim for 6.2–6.5, in coco 5.8–6.0. Wrong pH often blocks magnesium uptake. Use a Cal-Mag supplement in your feed – if you already use one, increase slightly. As a fast rescue: a solution of Epsom salt (magnesium sulfate) and water works very well as foliar feeding. Mix about 1 teaspoon per liter, spray under the leaves before lights off. This gives quick absorption and stabilizes the plant. Damaged leaves won’t recover, but new growth will come out healthy once the deficiency is fixed. I hope it can help you 😊

Think ph drift and calcium deficiency from it. Nutes are not avaliable, despite beeing presented. Triple check ph.

AutoPots are bottom-feeding systems, meaning water is drawn upwards through the medium. Over time, this can lead to a concentration of salts in the top layer of the medium, longer it goes more concentrated it becomes. Only takes 1 top flood feed to wash it all back down and potentially skew entire mediums ph/ratios/ec. First thing is checking ph, adding anything until we gauge ph is counter productive. You yourself should know if you did this or not. If not then continue with other answers. Good luck.

The pattern is a bit different from what I am used to seeing with Mg but it does look a lot like Mg to me. I also see some spots of circling death on the leaves making me think Ca could also be an issue. Want to review whats in your feed. NPK + CaSMg and ensure its getting proper amounts. If low. supplement, if adequate then you have other issues. Also want to confirm your PH is not off and that they are not sitting in soggy water. some brands of feed recommenced a flush when entering flower as they over feed a lot in veg. If your EC is high. You may want to follow suite on this.

looks like Mg deficiency she's eating itself a bit (although the new growth is fine) i'd suggest to add Mg 35 ppm per L ps. dont' fear, she's fine for now