most ich meds are copper based and you DONT want that in your tank it will kill any and all inverts in the tank and render your live devoid of critters still have the bacteria but thats about it,.
my suggestion is to get a QT tank set up to house new arrivals for a few weeks to make sure they dont have anything to spred into the main tank. its also easier to treat if something comes up later.
my best suggestion since you cant get to a supply place till tomorrow is to hope for the best tonight and treat him asap tomorrow. just read the directions and if at all possible take him out of the main tank even if you dont think you want corals right now assume you will later with any meds and supplements need to be a reef safe variety. trust me its adictive and very copmulsive hobby
Mike