+1 what rob said.

You know, a watched pot never boils. You will have that brown stuff until you realize you no longer have it. My whole tank was brown when I redid the rock and sand. The first time it happened I was like "What the heck is this crud?" this last time I was like "Hmm, my coffee needs a refill". It was gone before I knew it.

A diamond goby is good, especially over the dragon. Dragons take the sand and sift it at about three or four inches and leaves your rock and coral covered at about that height down. The diamond does the same thing, but they stay right over the surface of the sand so distributed sand isn't as bad.

Someone chime in... I believe that maintaining a diamond/dragon will limit the amount of pods in your overall system which could be problematic if you did want a dragonnet later.
To my own intent, I wanted a dragonnet. I got one of them physchedelic dudes the other day. I wouldn't get an engineer goby for fear that my pod pop would suffer for it.