It looks like your clown had brookynella (sp?) (aka: clownfish disease).
There probably wasn't much you could have done about it even if someone had responded sooner.
If your tank is over 40 gal. and has a decent clean-up crew (crabs, hermit crabs, worms, etc.) you don't have to worry about the body crashing your tank. If you have a brand new nano tank, it will probably cause it to recycle.