Hello and thank you for your message.
The best and safest way to treat this is to remove all the fish from the tank and put them in a hospital tank for treatment. Have a look at this thread about Ich on the Marine Depot Forums that talks about treating:
Now unfortunately for some the best way to treat the fish/tank simply won't work for them and they need to try using some type of medication in the tank with corals. Sometimes they work fine, other times they don't seem to have any effect on the ich. I have added some links below for medications that you may consider using on the tank:
Kordon's Ich Attack
Chem-Marine Stop Parasite
Ruby Reef Kich-Ich
If there is anything else we can do for you please let us know.
Marine Depot Customer Service