Root problems with Pleurothallids

[Flowers]

I've been growing Pleurothallids in a large terrarium for almost a year. They're alive and flowering, but have all but stopped producing new growths, and when they do, the new growths don't put out roots, and die. All new roots that start to grow die back shortly after starting or after making contact with their mounts. Other than air circulation, what could be the problem?