Good questions all and deserving of answers. If I miss any or if you have more questions, don't hesitate to post 'em:
1) Treating with copper is according to the medication instructions you are using. It is usually 14 days. BUT, during this time the copper concentration must be maintained in the right, therapeutic zone -- too low of concentration and it does no good (so you have to start over again); too high and you poison your fish. Make sure you use a copper test kit recommended by the medication manufacturer to measure their copper concentration, AND know what the concentration range should be.
2) No need to do multiple treatments. Choose one or the other. Using copper, I generally do lower the salinity a bit to make it easier on the fish, but not so far as to created water control issues.
3) After the two-week treatment, hold the fish in quarantine for at least 4 more weeks to verify that your treatment was a success. After that, if still no signs of the disease, the fish can go back into the display. HOWEVER, since you indicated that the disease was in your reef tank, then that tank should go fishless for no less than 8 weeks, IMHO. Then the reef tank is itself disease-free and ready to receive 'clean' fish. Hopefully, the clown was the only fish in the reef tank and you've treated it.
4) Marine Ich (
Cryptocaryon irritans) (MI) cycle info, in a diagram form is here:
http://www.petsforum.com/personal/trevor-jones/marineich.html
5) Your question about how fish can look good and still be infected can be a very long answer. The short answer is that the MI parasite actually prefers residing in the gills, which are invisible to your eye.
6) Depending upon the copper medication is the reaction of the bacteria to it. Generally speaking, beneficial bacteria and copper are not friends. I have developed strains of beneficial bacteria that are not bothered by my copper treatment. That is not hard to find --- your LFS that probably uses copper in their system, may have old crushed coral sand exposed to their copper, that contains these same strains. The use of such substrate though is not recommended and is a bit tricky for proper copper treatment. For your home QT, the 'beneficials' will likely die or go into a state of stasis -- not dead and not growing. Water changes will be your best approach unless your QT bio-filter has these copper-friendly strains of bacteria. Frequent water changes is a small price to pay for this 'shortened' treatment (use of copper) vs. use of hyposalinity. Have a sponge filter running in your display tank once its free of MI and then next time, at the end of a QT treatment of a new fish with MI, you can bring that over into the QT at the end of treatment, to act as your bio-filter during the 4-week observation period. Good QT advice can be found here:
http://reefkeeping.com/issues/2004-10/sp/feature/index.htm
I hope the above helps. :rollface:
