If a fish gets it what is the next step? Put in Q tank and use treatments or hyposalinity.
How quickly does it spread? Very quick
What if it is the only fish in the reef tank? Inverts are not affected by ich.
How do you dimiss it? Ich treatment and hyposalinity.
Best thing to do is becareful buying new fish. And QT before you put them in you main tank.
Examine them carefully looking for scratching, abnormal breathing, and salt looking parasites. Some fish are more prone to ich such as tangs.
You can find more info in the disease forum.