Air plants, as their name suggests, do not grow in soil, but merely need some form of support such as a tree. As a result these plants have to rely on the air or atmosphere for their water and nutrients. In their natural conditions in the wild water is supplied by rain, but air plants kept indoors will require regular watering. Often the reason for a sick air plant is the lack of water. I found an article by Stephanie Rose on her Garden Therapy website where she explains the best way of dealing with this problem.
Please visit Garden Therapy to read the article.