I have 2 orchids that I would really like to keep alive. I was given them for valentine's day. They looked great when I received them. However, the buds shiveled up and fell off after having the plants for about 2 weeks. Recently the leaves are turning dark brown on the edges and on the bottom of the leaves. The leaves feel stiff and healthy. I don't know much about this but I don't think there is any crown rot. The plants are potted in bark and I water them once a week. Any ideas as to what could be wrong with my plants?