ick follow up :(

Question
As a follow up to the question aout Ick/ich I asked before.  Diagnosing the  symptoms as ich (the pet store associate agreed), I added ich medication to the water as instructed.  The fish soon seemed stressed as shown by their clamped fins so I planned to discontinue the treatment today if it continued.  Today, I had to remove two dead goldfish from the tank, and the remaining are looking horrible.  Both seem to have bad ammonia poisoning (red streaks on tail) and one has finrot.  Poor creatures.  I'm afraid they'll both be gone soon, they're sitting on the bottom covered in white specks with horrible symptoms.  So, what did I do wrong and how can I fix it?  They original three have been doing wonderfully in the same tank conditions for three years or so, and soon after a new fish from a (legitimate) pet store is introduced, they all die off of various disease.  Time to start over :(.  How can I fix this next time?

Answer
Patty,

It is very important, as you have found out, that you quarantine any new fish before you add them to the new tank. This will last no less than 2 weeks. Unfortunately, I do not know what medication you used. The Ich might have been the disease that finally showed signs and was so far advanced that no treatment would have worked. In the tank that you treated, I would do a large 50% water change to try to remove some of the medication. Make sure the new water is the same temp as the main tank water so that you do not stress the fish even more. When treating Ich, heat is a huge help. Even though goldfish are cold water fish they can survive in warmer water while being treated. Some people even add aquarium salt to the tank being treated. To help prevent ammonia and or nitrite poisoning, always keep the water clean. Make sure the tank is big enough for the amount of fish you have and that the filter is made for a larger tank if keeping goldfish. This biggest thing is clean water. Goldfish are huge waste producers and bad water quality is the number one issue.