I use
fox farm and i feed them every 3 waterings they are exactly a month old..jus seems odd that the 2 biggest fan leaves are the only ones that look badif its mag deficiency but then again this is only my 2nd time..oh yea and its blim burn orka fem if that helps at all
At what level are you feeding? I'm hesitant to say it's mag def just because of its progression -- it's starting at the bottom. I feel the rest of the plant could be a bit denser green as well, but I also notice some leaf curling and tip burn. So it's likely lockout imo.
Full disclosure, I'm not a soil grower, at least not for cannabis. But, symptoms are symptoms all the same.
At a month old, a fan leaf like that dying is indication of more, especially with the brown necrotic spots. Something is either lacking or getting locked out and with the symptoms I really feel it's mag related.
Look up Mulder's chart and evaluate what you're giving the plant against what antagonizes or locks out those provisions. Another soil grower may come along and call me on my shit, but I'm just stating what I see.
What soil are they in?
Light burn will cause curling (you have some, not severe) and bleaching. The lighting isn't the issue.