I've fed all my houseplants tap water with a ppm of around 200. Never had any nutrient burn of them. "CalMag deficiency" comes to my mind when I am seeing your pictures (but I'm not 100% sure). But you have a so-called "drawstring issue" on your leaves, that is, they pull to one side, instead of being symmetrical. The progression of such a deficiency is the tacoing (folding up) of the leaves. I would give 50-75 ppm of CalMag in RO water. Good luck, buddy!