I bought my plant online. All the mouths of the plant were closed. The next day, 3 of them opened, leaving one still close. The closed one started two turn black around the mouth and on the leaf in one spot. After 5 days it still has opened and the blackness increases. But the rest of the plant is very healthy. How can I fix and if not fixable should I rip the dieing one off the plant or just let it die.