I have 2 strains that are doing the same spots but not the drooping. The first is orange bud that are almost 4 weeks into 12/12. From dutch passion fem. The second is papaya from nirvana. Almost 3 weeks old. Both stains are doing very well just a few spots mostly when they are young. Bottom leaves just a little spotting on the orange bud. From what I can read and learn it looks just like light burn spots but the young plants are only under flourescent. I thought maybe water spots that burn but I don't get water on the leaves. Anyway both are thriving, they grow out of it. Worrry more about the drooping.
The problem with MG is it 's full of nutes and every time you water you over nute young plants. You can't flush MG. It can work but it can kill just as easy