IMO if its at 84 allready just take the next two to 3 days and get it up over 86 and leave it there for a couple of weeks. That will kill off the ich. My tank just got over ich, mine was due to the addition of some new fish. I qtd them but the stress from moving them for QT to tank must have brought it on. But the heat only method wiped it out and i only lost 2 of the new fish and 1 female guppy who was very old.