We had a pair of bengaii cardinals that gave 14 bengaii frys. They're mouth broods, the male holds them in his mouth and for the next few weeks he will stop eating. As the fry grows you can actually see them poking out his mouth and eventually when the frys are fully developed, they will swim out. Beware that once the male is done, the babies have to be removed or the hungry male will eat them. Frys like to hang around urchins for protection from predators. My husband came up with this homemade urchin, since we didn't have one at the time. He used the glue gun and plastic toothpicks and manage to make a fake urchin. We placed the frys and "urchin" in the sump. We fed them cultivated brine shrimp eggs. When they get to be the size of a dime they can start eatin mysis.

I don't know about them been a dirty fish, but we still have the large male (4yrs. old) and two of his offsprings (2yrs. old). We had a total of three batches of bengaii frys, the rest went to LFS for store credit.

Here's an interesting link you might want to read.
http://www.reefs.org/library/talklog...ni_020799.html