I agree and I think about this often on this site.Hard to tell. My guess? Beginnings of K deficiency. But it's so small it's pointless to worry about unless it starts progressing.
If you were in nature and saw that plant you'd go, wow, that's healthy! Sometimes we become to obsessed with every wee detail. Still, best be vigilant
only issue is PH fluxuation ,5.8 in ,6.8-7. outIm using an gmb too and my voodoo juice and b 52 will be here tomorrow how are you liking them?
ppm was getting too high[1200ppm] in the coco ,I did a ro water flush to get it down,I agree and I think about this often on this site.
If I tried to correct every blemish that appeared on my plants I would have a giant mess. Sometimes it is what it is.
By the time you see the problem the plant has already found what it needed and requires nothing further.
But we start dumping cal/mag to it.