goldfish with other freshwater aquarium fish

Question
We started with a little goldfish from a carnival game.  He grew to about 3 inches and we upgraded to a larger tank.  We then purchased other fish from the pet store in which they asked if we had any other fish and we told them about the goldfish.  When window shopping at a second pet store I was told that I should not have the goldfish with my other aquarium fish.  Now I am not sure who to believe.  It's been almost 2 months now and they all seem to be fine together but I want to know if I should make some changes.  I do know that I need to upgrade to another larger tank based on the size of my fish when they are fully grown but have not done that as of yet because they are still new and small in size.

Answer
Krista,

 What you have been told is correct. Goldfish are cold water fish. They are also one of the messiest fish as far as waste goes. Most other fish, yours including i am thinking, are tropical fish. They need a heater where cold water fish do not. Most fish are good adapters to water temperature, but it will cut their life span down and eventually they will get sick. One goldfish needs to be in nothing smaller than a 20 gallon tank and that is if he is the only fish in the tank. The rule of one gallon of water per 1 inch of fish is no longer accurate. If you let me know the size of the tank and the fish in it, and the amount you have, I can let you know if you are ok or over populated. I hope this has helped and if you have any other questions don't hesitate to ask.