With the ammonia going up as it is, you should increase the frequency of the waterchanges. Only add salt for the amount of water you change. If you take out 50% of the water, only add 50% of the salt four your tank.
Roan,
Considering that the fish has dropsy, wouldn't Epsom Salt be better to use than table salt? Just something I was told.
If things are working well now, don't do anything different. Just keep changing the water. The fish having dropsy means that the water was loaded with bacteria and the fish became very ill. Both goldfish and plecos are notorius poop machines. To have them in such a small tank together is a disaster wating to happen. Each fish alone requires no less than 20 gallons of water to stay healthy with 50% water changes weekly. It is amazing that they stayed alive as long as they have.