Hawaiian skunk Strange leaf marks..

Hello there.. i m currently having a strange problem with my hawaiian skunk plant.. It's fimmed and has 4 top colas and 2 big side branches.. One of the side branches has a strange wilted leaf , i didnt pay any attention when i first spoted it. but i ve seen those marks on some more leafs and 1 is already dead.. I think it's low moisture with underwatering and low fertilising .. It could also be ph flanctuation since i was watering with different water trying to figure out which works best.. any ideas?


this is the plant




and this is the leaf i m talking about..

anything could help..

the pics are a little fuzzy, but if it like the leaf on the bottom of the third pics looks like burn to me.