This is probably not needed but if you're having troubles on the fight you can 'bug' it in some way.
If you kite Ick to the ledge he will eventually reset.
Now if you pull him again (fast as soon as he resets) -- he will cast explosive barrage but it will do nothing. IE explosive barrage will not show any animation and there will be nothing to hurt you while he casts it. The fight's most powerful spell is disabled.