Ram Puppy,
it looks like you have great ideas that I never even thought about. This could work out well if a quarantine was used correctly. At one single meeting you could get sand from tons of sources.

I know many wrasses make great flatworm predators. The downside to that is wrasses eat some of the good stuff too. As far as the canary in a mine field sps coral, Stylophoria and Pocilloporia are usually the first types affected by predatory starfish. I have no clue about the red mites favorite coral or what type it usually affects first. Hopefully someone will chime in with that answer.