dying goldfish

Question
i have had my two fantails for over a year and bought some redcaps from the local pet store, within two days they died and now my fantails are sick,the fins are ragged and they are drained of colour,i went back to the store and explained what happened they gave mea biological supplement and revitaliser tonic,the tank that i got my fish out of had a sign on not for sale, what else can i do to save my fish.

Answer
Well, you'll be relieved to hear that your fish are not potently sick, the worst is fin rot but it sounds like an imbalance in your tank. Check your Ammonia, Nitrates (or Nitrites), and Ph. If it's too high, a series of water changes over a period of time will cure that and your fish will get healthy again.