This is the time of year when the temperature fluctuations and we see a lot of ICH infections in our tanks. In a fish only tank the solution is simple, lower the salinity to 1.013 and add copper sulfate, preferably Cupramine, to a dose of .5 ppm. This normally will cure the ICH in two weeks with minimal loss. It is IMPORTANT to catch the ICH at the very onset to control losses.
Now in a reef tank things are not so simple. First off your coral and inverts will not tolerate copper, or low salinity so we need to use some of the new products on the market such as Herbtana, buy Eco labs. We have had success with this as long as you use 12 hour dosing. The best scenario is to remove most of the fish to a quarantine tank and treat them with copper, keeping the main tank fish free for 20 days giving the parisite time to die off in the main tank.
In any event if you have questions feel free to call us for further advice.