get RO water. buffer it to match your tanks PH, match your tanks temperature. then immerse the coral for 1 minute. (some people go longer I never go more than one minute and honestly I only use FW dips againts flatworms. so I cant say how effective they are against anything else)
DISCLAIMER: I am not advocating freshwater dips for corals, I am just advising the safest manner I know of doing an unsafe procedure, in fact I advise against freshwater dips.
second note: never freswater dip fish for treatment of ich, the ick is under the slime coat of the fish all it does is stress your fish and leave the ich unharmed. (I know your not asking about fish but I thought I would add that)