I'm wondering if I should just leave them to crumble away, or cut them them off. I heard affected leaves end up dying.
Those omnipresent deficiency charts were made by depriving plants of the various elements, then taking pictures of the results. It's uncertain whether they can be used in reverse to identify a deficiency from the look of the plant. If you are using a decent fertilizer, by defintion there should be no deficiencies. But over-feeding or wrong pH can lead to elemental lockouts that can be best fixed by correcting the underlying problems, not by chasing unlikely deficiencies.
I like to leave them on, just my thing. The reason I have for this is that the plant has currently decided which leaves it intends to pull the nutrients from. If you remove those leaves and haven’t successfully fixed the problem the plant will choose new ones to exhaust. Problems won’t be fixed until 3 light cycles. After that, if you firmly believe the problem is fixed, remove the affected leaves and see if the problem persists. What makes you think your problem is solely magnesium. Many times medium PH is the issue locking plants from selected nutrients. Adding calcium can also affect this as it gets loaded into the soil. The excess builds up and increases ph. Many soils in a bag come with a ph of 7 which is already neutral and no good for cannabis. Ruling this out can help you diagnose your problems further. Pictures would also help. Sent from my iPhone using Tapatalk
Should you suspect a Mg Def. simply add a TSP of epsom salts or calmag to a spray bottle fill with warm water and shake and spray heavy if you are correct the leaves should return green within 30mins good luck
Exactly what he said. If it's just magnesium deficiency they're repairable. Calcium is another story.