Hello!

Unfortunately, your tank is very overstocked. One goldfish needs at least 10 gallons to themselves, with no other occupants. Pet stores often give the wrong advice. When you have this many fish in a tank, even if you do weekly water changes, your fish are being exposed to harmful water levels. Here is the link to the Goldfish Faq and the Goldfish Care Sheet. Is there any way you can return some fish to the pet store or get a larger tank? Also, goldfish are pretty specific to a certain type of tank and are not meant to be kept in the traditional "tropical fish" setting. Here are some quotes from The Goldfish Faq that I linked to above:

"Goldfish are coldwater fish and need a specific temperature range, which is typically lower than that required of tropical fish. Likewise, other fish may have different pH, hardness, food, etc. needs.
  • Goldfish need a lot of dissolved oxygen. If there are fewer fish in the tank, then there will be more oxygen for your goldfish.
  • Goldfish produce massive amounts of ammonia. If there are fewer fish in the tank, then there will be less ammonia produced overall. The ammonia that goldfish produce may harm other fish, especially the more sensitive ones."
You may be having problems with Swimbladder Disease if your goldfish are having problems with floating too much at the surface or hanging out too much on the bottom of the tank.

The bottom line is that you need a larger tank, or the goldfish will have to go back to the pet store. 4 goldfish need a minimum of a 40 gallon tank. It sounds like a big surprise to most people, but goldfish produce tons of waste and need high oxygen rich water, which is why higher temperatures can hurt them. Water holds oxygen better in colder water.

If you need help on how to set up a new tank for your goldies, we're here for you. If they aren't moved to a larger tank and separated from the tropical community that you have, they are going to get more problems other than swimbladder and they wont make it. Fancy type goldfish can get VERY large. People usually think that the "feeder fish" get to be big. While this is true, the fancy types also get very big!