Brown/black leaves on Ang. distichum - what to do?

[Leafmite]

I have mine in a bowl with a Lepanthopsis and some other miniature orchid. The distichum is in the middle, where the bowl is open. The mini orchids are to the side so they get more humidity. Lava rock is at the bottom, NZ sphagnum moss was laid on top and the orchids are all planted in the moss. I put a little bit of a different moss culture in the bowl, too, and it has spread over everything to improve the appearance. When I water, I water to the side and let the rocks wick the water to the moss. I have been using distilled water with the occasional addition of Cal-mag and a little Ironite. I have some eggshells in there, too.