When the cattleya puts out a new growth, new roots will follow. If it has at least one new growth starting, it will recover easily. If it doesn't, and you go the lava rock route, you can water the lava rock to provide humidity (the orchid is on top of the medium so won't rot). That will help keep the psedobulbs from losing too much water until there is a new growth. You can also put a clear bag loosely over it and keep it warm (air it out a few times a day). Good luck!

---------- Post added at 09:47 PM ---------- Previous post was at 09:20 PM ----------

Most people recommend cal-mag as a good choice for adding calcium. Some add oyster shell, too. I add eggshell.

How do you add egg shell? Just like crush it up into a powder?

Eggshells release calcium slowly as they decompose. I just break them into pieces and mix them in a bit with my lava rock. I like that they don't wash through my medium and that they deliver a constant supply of calcium. If you use bark, lime works well, too. Or, you can buy a fertilizer with calcium. I bought the MSU fertilizer last year. Still not sure if it makes a difference.

If you water your orchids with tap water, there is probably enough calcium in the water so you don't need to add any. If you water with rain water or distilled water or RO water, you'll need to add calcium and magnesium. If you're using one of the pure waters then you can buy a fertilizer that contains calcium and magnesium or you can get a cal/mag supplement used by hydroponics growers and give it once or twice a month along with your fertilizer.

Hmm... Maybe I'll try egg shells?
Currently it's in spag moss, but I will eventually switch to bark/husk/and some other stuff mix.
We have a filter on our faucet so I'm not sure how much of what gets thru. It's supposed to filter minerals and stuff I think.