Plant in need of diagnosis: Any wisdom to share?

Hi there, Camila from the U.K. here. This is my baby Ziggy. He is an Alocasia Zebrina which I purchased at a local garden centre and he has always been a delight to care for. Super happy and perky all the time.

Unfortunately, I had to leave him for a while under a housemate’s care and this guy managed to practically kill Ziggy in a matter of weeks. So as soon as I returned, I tended to him and managed to get him back into shape. (A true phoenix emerging from the ashes). However, I’ve noticed these black spots under his main leave along with a weakened texture of the leave. Nothing noticeably different of the top though. Does anyone know what this is and how to treat it? I’d like to give Ziggy a fighting chance!

❤️

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