Awhile ago I repotted a Nep of mine into a mix of 25% lava, 25% charcoal, 25% sphagnum, and 25% coral. I thought, what's the worst that could happen? There was a thread in another forum that discussed the benefits of putting a thin top layer of coral on top of Nepenthes pots; it was supposed to encourage stronger, more succulent growth. So I decided I would try it as a part of the actual media.
That's after a few weeks. The N. madagascariensis that was in there had more than half its leaves burn off, its root system suffered, and the growth tip shriveled. I thought it was just shock from being barerooted. Although that may have been a contributing factor, it was not the main variable.
I learned the hard way, lol! Lesson learned: Use coral sparingly, and try not to put too much in your Nep media!