QT tanks are a must, the reason the meds arent working i would guess is because the tank itself is still infected and keeps re-infecting your fish. The way i have always understood ick to work was that the white blisters on the fish were the eggs of the disease and when they burst they would float around the tank infecting anything and everything because they would sit on the substrate of your tank and it is a never ending vicious cycle that why you need a QT because it allows both your fish and tank to recooperate, the ick in the tank has nothing to feed on so it dies out withing usually 2-3 weeks while the fish in the tank have nice uninfected water and are usually being treated, its the best way to deal with it, everybody please feel free to correct any incorrect info here, hope this helped, so before you buy anymore fish you better buy a QT tank otherwise you will be throwing away your money and killing otherwise interesting fish
Brahm