Dolomita for Orchids

[Ray]

What he said.

I recommend against it in S/H culture because the particle size is likely small enough to clog up the voids, suffocating the roots, and ultimately filling up the reservoir.

As a general note, from a nutritional perspective, there is nothing unique about S/H culture. A plant needs the same nutrition no matter how it is grown. What you should be concerned about is the mechanical properties (size, shape) of things to add, and the impact they may have upon the technique.