This sucks. The green mandarin I purchased for my step-father's tank passed just recently.
Without remembering what formaldehyde does to shrimp, and liverock -- he dumps a cap in to treat the disease caused by stress on the 3xYellow tangs, and imperator angel -- after the regal tang had already passed. This knocked out both shrimp, and the imperator died anyway. Formal' also destroys organisms harboring in liverock -- thus effectively killing off all of the mandarin's plentiful food supply.
A moment of silence for a known hard to keep fishy that was prospering so well...
....and a word to the wise, mandarin's a much easier to keep then one would think, as everything leaves them alone. Just make sure you have a developed tank, and plenty of live rock supply. Also, I now know the importance of a quarantine tank to establish the health of newcomers. Especially those from the LFS
-- if you are to medicate (as a last resort only), please be sure that you do so in a QT
, nor be afraid to give your infected fishies an aerated FW
cleansing for >15 minutes.