Treated for ich

Question
I have a 20 gal freshwater tank that has been functional for about a year now. The two feeder style goldfish that i originally got to cycle the tank are still with my tropical themed tank. The Goldfish Cylde became lethargic, secluded, and would hold his dorsel fin down constantly, but would still come up for food and showed no physical signs of illness. Recently Bonnie (the other GF) started acting the exact same, and overnight they had white spots on their fins. All internet sources pointed to this being ich. Rasboras and tetras share the tank with the GF. So I went to the local pet store and bought some of the blue stain type ich treatment and pulled the filter out. I already keep the tank warm 82 f. So this was at 8 PM, woke up at 6 am and Clyde the originally sick fish... is seizing on the bottom of the tank and half of his tail was gone. Did I treat for the wrong thing? I know he's a 10 cent fish, but I don't want to kill him off.

Answer
The problem I see is you have cold water fish with tropical fish. 82 degrees is too warm for the goldfish. They like to be in water that is about 64 degrees. Having them in a tank that is too warm for an extended period of time is not good for them however, the fastest and safest way to treat Ich is heat and salt. Slowly turn the heater to 85 degrees and add some aquarium salt to the water. With the higher temp. it forces the life cycle of Ich to speed up. We want it to be in the "swimming" stage. With the heater at that temp, and the salt, it shortens the Ich life cycle to 2 to 3 days. In colder water, it can take up to a month. The ratio for the salt is 1 teaspoon of dissolved salt to 1 gallon of water, or, 1 tablespoon per 5 gallons of water. Make sure the salt is dissolved before adding it to the tank or you will burn your fish. Also, only add the salt to the water that is being replaced during a water change. Once the Ich is gone, you can slowly turn the heater back to 82 degrees. I would also remove the goldfish and put them into the right home. The two goldfish should be in a tank no smaller than 30 gallons with a filter made for a larger tank. Ich is 100% preventable by doing weekly water changes. With goldfish, it is very important to do water changes every week by removing 25% of the water, by cleaning the gravel, and replacing it with clean conditioned water.