Many of us found out the hard way Prosthechea and Anacheilium want to stay between wet and moist. I now use S/H for them, or if in bark stand the pot in a shallow dish of water. I think sphagnum would also be great for them.
If potted in bark or sphagnum, the medium will age rapidly, and repotting will be needed every 1-2 years.
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