saltwater fish disease

Question
I have a reef tank and purchased a snail 4 weeks ago. Within 3 days of adding the snail my butterfly became covered in a dusty film and died. Two days later the other two fish in the tank also had the film. I began treating with Maracyn (used full treatment and didn't work) I then began treating with seachem sulfathiazole. After 3 treatments my angel looks better, but the clown looks worse. My coral banded shrimp fell apart and died and my mushroom corals are shrinking rapidly. I moved the clown to a QT and have treated 2 more times. Still no results. What should I do to treat this?

Answer
Hey Kim

I think the fact that the fish became sick after the snail is just a coincidence. How are your water parameters? Any ammonia might have stressed the fish, and caused the film. The film can also be caused by a sudden salinity drop or increase. Does the Seachem med have copper in it? Copper is fatal to corals and inverts, if you added it to the main tank, that seems to be the reason why your mushrooms shrank, and your coral banded shrimp died.

Try to get all of the sick fish into the quarantine, continue treatment with the seachem, and if the seachem med does have copper, do a large water change on the main tank. Also, if you can, move the mushrooms out of the copper water. If none of the medications contain copper, please give me a update and i will try to further help you