Douglas fir bark is the cornerstone for almost every orchid potting media out there. Until it begins to break down (1-2 yr.) it retains practically no moisture whatsoever. That's why it has been used for many decades.
Superthrive is not a fertilizer, it is a hormone mixture and most people think the advertisement of it is a bunch of hype and that the product is of little value. There is absolutely nothing wrong in using it up, but mix it in your water or in your diluted fertilizer.