The stink is from fish waste, I would wager. Not so much the ammonia (you'd have truly obscene amounts before it started to smell) but from the decaying organic matter. Goldies produce tons of waste, they're messy, and if it's just sitting there decaying, building up, well, I think you can imagine how it would smell if you lived in a small cell with just a bucket in the corner, dig?
Don't take that as a slight, I've been massively overstocked before I learned better and I don't think badly of newbies who do. Goldfish need very large tanks, but our society is saturated with images of goldfish bowls and with the notion that fish will only grow to the size of their environment. While technically true, it's in no way a good thing.
Since your tank is still pretty new, consider a more concerted stocking effort. A 10g is a really small tank, so instead of having numerous fish species, try only 2. Maybe guppies and cories or perhaps barbs and cories? Just a suggestion. Since you're fishy cycling, getting rid of some of the fish will make your life much easier, I think that you'll like the end result much better as well with only a couple of species with their populations built up a bit.