Is this tank cycled?? cause if it aint using meds would be a lot harsher to your fish and your biological filter....If i were you I would use the heat and salt method....Raise your temp(gradually) all the way to 30 C/86 F and add 2 tablespoon of salt per 10 gallon and keep it that way for 10 days and when all the ICH spots are gone keep the heat for another 3 days before bringing it down also make sure that you have extra airation or something to circulate the water cause at this temp there is less oxygen.....goodluck....I'm currently having mild ICH breakdown on my tank and this method is working all of the ICH spots are gone except for my Clown loaches which has a couple of spots.....