2 things come to mind-
- damage from hitting the side of the pot when the fan is blowing on it, most likely at night when the leaves are lowered,...... or
- damage from being too wet due to sitting in a suacer of water for too long.
I do not think it is nutrition related, but without a diary and/or a lot more details, it is hard to say exactly what, because no one knows what else you are doing/not doing.