Actually Dendrobium Fire Wings is 3/4 Latouria and 1/4 Phalaenopsis
Type. I grow this hybrid and treat it as a Latouria, water it well and never let it dry out completely.
It has slender roots and should be in a fine mix. Carol, your seedling mix should be great for this type of Dendrobium. Plastic pot might work better then clay.
Fertilizer regularly at half strength. Blooms spring and fall with more flowers in the spring. Never hesitate to ask me anything about orchids. If I don't know the answer, I can get it.