Sick Fish

I bought a couple new goldfish (forgot the actual type) yesterday and
noticed today that one was just floating below the surface and not really
moving much. He wasn't gasping and would occasionally swim around, but for
the most part, just floated. I separated him from the rest and now tonight
he is laying on the bottom of the container. He looks like he "might" be
slightly bloated, but not significantly. I can't see anything else wrong
with him.

I am going to bring him back tomorrow, but anything in the mean time I can
try? Someone else mentioned on another thread using salt? Will this work?
It can't be table salt though, right? I think that is all I have.

Scott