Definately get a Qt set up and begin treating the fish if
you are possitive this is ick and not something else caused by the water problem. This may be a blessing in disguise sorta...
While the fish are being treated it will allow you to get things sorted out with the problems in the main tank hopefully. If possible I would suggest a 20 gal
QT but be sure of what you are treating.
One other thought (all I have left are guesses), use any anti-biotics or similar products in the main tank? Or possibley obtained something from another hobbiest?