How to save my dying tetra?

i changed his water last night in his 3 gallon tank. he is the only fish in that tank. after i changed the water he was pretty much sick right away. he is at the bottom of tank, and looks dead, however his gills are slightly moving, so he looks like he is barely breathing.. before i changed the water he was fine, so i am guessing the tap water i used for the change has too much chlorine or ammonia or somethng, although i kept about 50 percent of his old water in there. it is WAY to late to go buy anything, plus i do not drive, so what can i do..... here is what i have..... aquarium salt, which i already put in when i changed the water, before he was sick, and i also have a bottle of liquid fungus cure....... HELP!! maybe some household remedy??