Clinton, I've heard that you can keep about 32 small to average sized fish in a tank that size. I've also heard that it's one inch of fish for every gallon. Going by that, and considering the tetras are about half an inch each, I think the numbers add up.
The one inch rule is only a general rule for fish that stay small, and a lot think it's outdated. The one inch rule may work for tetras or danios, but it definitely won't work for cichlids, larger catfish, piranha, goldfish or any other medium to large fish that people keep.
Its also assumes all fish pollute at the same level which obviously isn't the case...try comparing a large pleco or goldfish to a similar sized Angel etc...the first two are poop machines compared to the Angels It also doesn't account for plants or other structures you have in the tank or really even the shape (surface area to volume ratio)