I've got some yellowing on the tips of the upper leaves & the bottom leaves started out with just the tips but have since went around the edges of the leaves & a couple leaves have died off. Hopefully someone can tell what's going on from the pics. Everything I read says too many different things can cause it i.e. overwatering, lack of nutrients, too many nutrients, lack of nitrogen, etc. How do I know which thing it is so I don't treat it for the wrong thing ?