I had a very bad case of ich a few months ago. I raised the temp to 86-88 degrees for 2 weeks, no chemicals, and they all turned out fine. Even mu delicate plecos.
Like Water said, try to found out what caused this and prevent it, what is your water parameters, food you feed your severum, tankmates, any wild caugh fish in your tank. Then do a HUGE WC about 80 percent, to try to get rid of the infection. My oscar and pacu had the "ich" too and everything was good until i saw sometimes moths in my house gets attracted to the tank and there r holes so it can get in. Once in the dampness of the lid makes the moth fall into the tank. Then the fishies eat him and they get infected.
I also recommend feeding one of the NLS Thera A pellets during this period and in the future. Decide which pellet size works best for your fish and start on it immediately.