Welcome to Reef2Reef!
Your powder brown dying and this fish being moribund could well be related. More history is needed to try to work through that though. This post explains all that:
Aquarium Fish Disease Problem Solving Determining the best course of action for a problem with your aquarium can be a difficult task. Even advanced aquarists will often need to seek the help of others for complicated or unique issues. Our intent here on Reef 2 Reef is to offer expert advice...
www.reef2reef.com
Specifically, how long did you have the powder brown?
What other fish are in the tank now?
From the information at hand, I would say that the tank has skin or gill flukes. the timing and the scratching all add up. Flukes don't kill fish suddenly, but the symptoms they cause are pretty subtle and easily missed; rapid breathing, scratching and pale coloration.
Jay