Another Newbie Question: Are copepods the tiny white barnacle looking
things that coat the rocks, etc? (That's what the guy that I bought the
tank from told me.)

Then I'm looking at this:

http://www.reed-mariculture.com/copepod/

And, they appear to be a free floating insect like creatures.

Reason I ask is that my Mandarin Dragonnet isn't looking very good. (It
was also beaten up by a damsil). As far as I can tell, all the white
crustations on the rocks (which it was eating) are gone.

--Kurt