Spots on leaves?

[Bom Shiva]

I have an NLxBB on day 48. I flushed her yesterday morning and noticed these spots this afternoon. They don't rub off. No mites or anything crawling. It's only on a few upper and middle fans...??

I just read an article that said if your flushing with purified water, to bring the PPM up to 100 before flushing, as a 0ppm water will strip all nutrient quickly and cause unintended deficiency instead of lowering the nutrient/salt content