For starters, Blue is right about the Goldfish
not working in a 3 gallon bowl. There is probably a huge problem with oxygen depletion in this bowl unless you are running a filter or air stone. Goldfish
are heavy consumers of oxygen compared to the average "tropical fish".
The salt was a good thing, so long as it's not too much or too often. Salt is good for medicinal purposes, it acts as a healing agent, but is not something to use continually for Goldfish
, as it will cause health problems.
When you clean the bowl, how much of the water are you changing at a time and how often? Are you acclimating the fish into the new water or just plopping it into brand new water each time? You can cause shock by just dropping a fish into clean water without acclimation.
Also, how often are you feeding, what kind of food, and what is the temp? All of these things will also have an effect on your fish, especially considering the environment it's in.
For a situation such as yours, I will suggest a daily water exchange of 50%, keeping the water room temp. Treat the new water with water conditioner, such as AquaSafe, by tetra. BE CAREFUL NOT TO OVERDOSE THE CONDITIONER. This can kill your fish quickly, and it's a horrible way to die. Talk to your LFS, see if they will take the fish back and maybe exchange it for a betta. Remember with the betta... 1 fish per bowl! In a 3 gallon bowl, so long as it is kept at above 70 degrees and below 90 degrees, kept clean with a weekely water exchange of about 20 - 30%, fed every other day with betta pellet food or live blackworms/bloodworms, or live brine shrimp, it should thrive.
There is NO other fish I would suggest for a bowl with no filter or heater. If you decide to add an air pump and filter (PenPlax designs one for use in bowls, it has a snap in cartridge with sponge and carbon, once each month you change the cartridge), then you could work with a small school of about 3 - 5 white clouds or danios. The kinds of fish able to thrive in a bowl are few and far between. Most fish small enough for that size of a container will need a heater, the danios and white clouds the only exceptions. All others beside the betta will need a filter. You can actually do quite a bit with 3 gallons if you add heater and filter. It sounded as if space was your only issue, not funding? If that is the case, let me know and I can teach you how to add what is needed and turn it into a "tropical tank" with filter, heater, and up to 5 bright colored fish, live plants, the works... I have fun setting these up because so many people think it's not possible to do in a bowl. A container is a container, it's what you do with that container that makes it different from the rest.
Hope this helps....