Treating Ich with copper is mean. Copper and a tang's stomache do not get along. The best thing to do is treat with Hyposalinity. I had a breakout last year because i didnt QT a new fish that i put in my display tank. Here is what I did and I have been ich free for about a year now:
1. Get a QT big enough for all your fish. I have a 55 bc I have tangs.
2. Purchase a filter that is 2x the rated capacity of the tank
3. Place the filter media in your sump/fuge for 5 days. This will let some nice bacteria from your tank start to grow in your filter media and help with the initial cycle the tank will have.
4. Fill the QT with 1/2 tank water and 1/2 with new salt water
5. Adjust temp and salinity to match your display tank
6. Transfer all the fish to QT. You must get all the fish out
6. Start dropping the salinity slowly until you reach 1.010.
7. Monitor the pH, amonia, and nitrates of the tank daily.
8. Change 10% of QT water volume daily
9. Keep salinity levels at 1.010 for 4-6 weeks after last visible parasite is gone. Keep main display tank fallow.
After the time is up, slowly raise the salinity back up and get them back to their home.
And another thing, ich is not present in all aquariums. Ich is a living parasite that goes through 3 life cycle stages. One stage it is living in the rocks and substrate, one is a free swimming stage, and the last is the hosting stage with a fish. These cycles are repeated approximately 10-14 days. If you remove the fish from your display tank, the ich will not have any host and they will die. That is why it is important for you to remove all the fish. Ich will not survive if you do not have any fish in your display tank.
Like it was mentioned abouve, you need to QT EVERYTHING that goes into your display tank. It is possible to bring home a piece of rock or coral from your LFS with some nive ich eggs on it.
