When the plant is weak and roots are bad, the cure can be very recalcitrant. Here is a new soft yellowish leaf oc C. skinneri with tip dieback caused by Ca-deficiency. The other leaf of this bifoliate species is already lost, and both leaves of last years bulb as well.
The other plant is C. labiata. Roots are bad, with nearly no new root growth. Last years bulb lost its leaf quickly. This years bulb is stunted.

Excellent pics! They definitely help people ID this problem and you're right about the cure being difficult. Simply reversing Ca deficiency can't cure the growths that have suffered from it and the plant can suffer immensly as the new growths and roots are stunted or just don't grow.

This is a great post! I hope everyone reads it.
I learned about calcium deficiency the hard way. I had always used my pond water (the fertilizer for lotus and lilies is high in calcium) to water my plants during the summer and when I gave up having a pond, I began to use rain water. I didn't realize that my orchid fertilizer wasn't complete as most of the fertilizers I used for my other plants. I lost quite a few of my cattleyas and a couple of other orchids to 'Black Rot'. Yes, I felt stupid when I realized what had happened (I grow many other plants) and began right away adding calcium. I haven't had a problem since. Now, I try to warn others so they don't go through the same trauma.

I'm trying to rescue some catts that I thought had been underwatered, but are actually showing all the symptoms of Ca deficiency. They're now mounted on a cement composite wall, so they're getting plenty of Ca, and new growths are coming in nice and green. They're still stunted, though, so it will be a long road to recovery.

I'm loving this thread. I went right out and got my gypsum out of the shed had Epsom salts in the basement. So I mixed some up my gypsum is pelleted so it took allot of shaking to get most of it mixed up.

Question is gypsum better than dolomite lime as I have them both. I use them on my yard and garden. I have read on here about the lime as well and have put it in my phrag and paph just the pellets.

Dolomite lime will make epsom salts unnecessary. It has cal and mag in the right proportion.

Gypsum & Epsom salts are both readily soluble, whereas the dolomitic lime (limestone) is slowly soluble. Also, G&E will not change pH (at least not by much), whereas the DL will increase pH. Part of the reason that DL is applied to lawns & gardens is to modify pH.

This is true! However, Roy Tokunaga at H&R was telling me that he sprinkles dolomite on top of orchids potted in spag to keep the pH at the correct level. If you've ever seen spag with a slimy film growing on top, its a sign the pH has gotten too low. Dolomite will prevent this. I think for plants potted in spag, sprinkling the surface of the media is the simplest way get the correct amount of Ca/Mg to the orchids.

A dissolvable application of Ca/Mg is probably better suited for all other media, though I'm sure there are people doing just the opposite with good results.

I use Botanicare CAL-MAG Plus, but I also periodically use a pinch of Epsom Salts in my mix to supply a little sulphur, which is lacking in my local water supply. J. R. Peters Lab states that my water has about 9 ppm sulphur and 10-80 ppm is normal range.

One caveat they give about adding Epsom Salts for sulphur: "DO NOT MIX any sulfur-containing compounds with calcium, an insoluble precipitate will form." I don't think that's a problem as long as I add the Epsom Salts to the diluted mix; in other words, don't combine it with undiluted Cal-Mag or you will lock up the calcium in a precipitate.

Thanks for posting! The pictures are really helpful. I think a few of my orchids need some calcium.