Help! My goldfish are in trouble!

Question
Ok so we have had these two goldfish for a year and we have put them in our pond in the summer and then in a tank for the winter. Well they had started to get too big for their one tank (10 gallon) and so we moved them to a 50 gallon. (the smaller tank was in one of our back rooms that doesn't get a lot of people traffic and the bigger tank is out in the living room where people are walking by a lot I didn't know if that had anything to do with it). One is about 6 inches long and the other is about 5. Well the first week we put in a small catfish which ended up chasing the goldfish so we immediately switched him to a different tank and put in another one that didn't chase them.
The second week they were doing great swimming around and not having any problems and then all of a sudden on the third week one of them just started convulsing and then she would float vertically for a little bit and then return to normal and they both started being really lethargic and staying at the bottom corner of the aquarium. So we decided to switch them back to their other aquarium but we haven't seen any improvement. They are still just as lethargic and the one's back fin is slightly shredded. Also both the catfish died.
The water temperature in both is the exact same at about 70 and then the water pH and alkalinity we really haven't tested for so we don't know. Any ideas????

Answer
Hi Amanda,
You can't keep catfish with goldfish. Catfish are warm-water fish, while goldfish are coldwater fish. Catfish need heaters, but goldfish cannot live with a heater. (Catfish - 75F +, Goldfish under 68F)

I would advise changing 20% of the water immediately, an since I don't have a picture, I do not know what is wrong, but I would add an airstone just in case, for extra oxygenation. Since there are no catfish to bug the goldfish, I would not worry about the torn fins, if it was from the cats.

Check out this link for disease diagnosis:
http://www.fishlore.com/Disease.htm

I would buy a broad-spectrum antibiotic. Try seeing the link above, to properly diagnose the fish. Once you have, buy the appropriate medication. You will want to buy an ammonia and nitrite test kit, because it may be due to an ammonia problem. Keep doing 20% water changes every two to three days.

It may be swim bladder disease, because of the awkward swimming patterns. The catfish died because they cannot be kept in cold water.

I hope your goldfish recover!