Your quarantine tank doesn't need to be pretty. A big rubbermaid trash can (new obviously and rinsed out with white vinegar and RO/DI water before using) will be fine. Buy a small air pump and stone and a heater for circulation and temp control. Go to
www.wetwebmedia.com, this site and others for treatment protocols. I have used cupramine very successfully on my tang and rusty angel. Get a test kit to monitor copper. This is a pain because the test kits are all almost impossible to read. Seachem makes one that I could at least read, though not easily. Hyposalinity can work if you have a refractometer and get your salt content just right and many experts recommend it. I just find Cupramine easier. Even if you use Cupramine you can go for mild hyposalinity (like 1.019) to help discourage ich but this level isn't enough to kill it. Treat for several weeks, as recommended, and make sure you treat ALL your fish at the same time. You need to remove all fish from the tank for some weeks (4 is minimum. I prefer 6 to 8 weeks). Keep doing water changes since you won't have any biological filtration and use something like Amquel Plus to remove ammonia and nitrates. Replace Cupramine and Amquel Plus with each water change. Once your treatment cycle is done, do a big water change and throw in a bag of activated charcoal to remove the copper. After a few days, replace the charcoal if you want and add some Colonize or other bacteria to start a bio filter. I keep using the Amquel Plus just to be sure. Keep checking the fish to be sure ich is gone (if that's what it is). After 6 weeks, all ich in your tank should have died off (no guarantee but it usually works). Snails, shrimp, corals and crabs won't allow ich to thrive so no worries there. Put your fish back in. Don't tranfser any of their treatment tank water. Do a rinse with your display tank water just in case any copper remains in your treatment tank. Good luck! P.S. this probably seems like a pain and it is but not as bad as you might imagine. If the fish are healthy enough to survive and if you have the right diagnosis, you will be glad you did it.