Hi weekend gardener!
Hey Vanda lover - I have never heard of charcoal chunks before - how well does that work?
I myself have switched over completely to coco husk of various sizes. There is a compressed 'brick' of the coco husk that is being sold exclusively for orchid medium, but it is somewhat expensive.
Living in Indianapolis I have the luxury of going to various nurseries and hydroponic stores within easy driving distance. I have found that hydroponic suppliers have large "bricks" (12"X12"X5"), in a variety of chunk size. I paid $10.00 per brick, much cheaper than the smaller orchid-specific bricks; plus, I was able to get medium chunks for my larger orchids and a seedling size that is great for the smaller ones.
I have blended it with other medium such as bark, and it works very well, but most of my orc's are in straight coco chunks or fiber (the ,ong fiber allows more air flow - my plants love it!). I also bought a bag from a nursery that was sold as mulch. It has a large variety of size in it, from small fiber to larger chunks, and it seems to hold the water better for my moisture lovers.
My house is very dry by nature and the bark was just not cutting it, even with sphagnum mixed in. But the coco is great at holding the moisture in all the sizes of pots I have it in.
Others will have different experiences, but I swear by it. I think it is a good idea to be sure and soak and rinse it well before you use it. I add mild fertilizer to the water and it seems to help the transplanting stress.
So, yes, coco husk is being used in orchid growing a lot now.
Let us know what you decide and your result!
Steve