Lithopsman, it sounds to me like you may have inadvertantly over potted your orchid. From what size pot did you move it and what size did it go into?
The plant you have has a sympodial growth habit, that is it produces pseudobulbs on a creeping rhizome. The Phalaenopsis on the on the other hand is a monopodial, it does not produce a rhizome but adds growth only to the top of the plant.
So I assume when you say you have multiple plants you are confusing each psuedobulb for an individual plant.
While I aggree with most everything Josh said I would add this, slab culture can be difficult for a begginer when he or she has no previous knowlegde of how a particular orchid or any orchid for that matter behaves to differing stress factors.
One should first have at least some experience with orchids in standard pot culture before attempting to grow them on slabs.
As for peat I dont like it with bark, it is very acidic and therefore assists in the decomposition of the media, it can also cause ph shifts which can interfere with the absorbtion of nutrients.
I prefere a fine bark mix composed of fine fir bark-60%, vermiculite-10% and large grain perlite-40% with a little fine charcoal-10%.
You definately need to add more perlite to your mix.
FWIW