Black discolouration on leaves

Personally I can't see a REAL problem, no plant will have 100% perfect leaves, 100% of the time. Some of the damage I could see looks to be caused by the leaf rubbing against the side of the pot when the fan is going and the spots to me seem most likely caused by bi-carb soda drying on the leaves and this leads to blocked stomata/leaf pores which results in the small brown circles of death/necrosis. I do not believe the answer to nearly every problem is cal/mag. Any decent nutrient solution designed specifically for cannabis should have ample amounts of both these minor nutrients for plants not to be lacking these items. Cal/mag is really only needed in increased quantities during flowering, and again, any decent flowering nutrient designed for cannabis should have adequate amounts of these two minor nutrients. I do not believe you are at any risk of "losing her" as I personally can't see anything wrong with your plants apart from the rubbed areas and the necrosis caused in no doubt by the foliar application of bi-carb or even by splashing nutrient solution onto the leaves when you are manually watering/feeding them, as this will have the same effect as the dried up bi-carb, leaving mineral salts on the leaves. Removing otherwise healthy leaves will not solve any problems, real or imagined, and only reduces your plants capacity to produce energy that she needs to grow her best and biggest. They also need adequate levels of nitrogen, so go back to feeding them as normal, your plants seem to be lacking nitrogen at the moment as they are quite pale green, but try not to over do it with massive doses. Try quarter strength 2-3 times a week and that should be plenty and stop the bloom nutrients. They are for when your plants are blooming (!) and could also be a cause of any problems you think you could have, by providing excessive phosphorous and potassium for your baby/young plants. An excess of nitrogen will not cause spots on leaves, the leaves will go entirely brown from the edges inwards to the centre of the leaf and looks like dried fall/autumn leaves from deciduous trees. Hope this helps,... Organoman.

Increasing the calmag will stop the issue. Those burn/rust looking spots won't go away but by increasing the calmag should stop it. I would also continue feeding nitrogen by doing so it'll just add to the plants health than do more harm by decreasing it. Happy growing