AsNoriuanswered grow question 3 months ago my first idea was calcium and ph swing, but it forms totally different, you have spoting on other leaves ( in middle of it ) so its not mechanical/ physical related. some plants shows random pigmentation, but its too uniformed. calcium would bring more rusty spots, spots, not lines. if you pour water over leaf, check how its holds, think thats the case ... its interesting for me too, thats why i write so much. had millions of issues, but this heavily confused me.