epiphyllum leaves turned black and shriveled up
Most of my epi's leaves are turning black.
Certified GKH Gardening Expert
This is usually a sign of being overwatered, and infection starting in on the plant. These will do best in a light soil mix like you would for orchids, or cacti, but with a little compost mixed in. Most potting soils will be far to heavy for these plants on their own, so it must be amended with something to lighten it up a little.
It will be best to cut off any infected portions of the plant and mix up a solution of 1/4 peroxide to 3/4 water and water this in once. Make sure that the top two inches of soil are almost completely dry before watering this again.
This article will help with the care of these plants: https://www.gardeningknowhow.com/ornamental/cacti-succulents/epiphyllum/epiphyllum-plant-care.htm