I purchased 3 dendrobium plants last July from hhome Depot. The plants were healthy and did bloom. They have grown since and are in a huge west facing window. I live in Pensacola, FL so light is no problem. About 2 weeks ago i started to see tiny black spots on the leaves. The plants are healty and are in the original potting medium of bark. What do I do? have they cgotten some sort of fungus.