Thanks for all the help guys,
just to answer some questions, the real story is a little more complicated than the one i told.
basically, my friends ten gallon tank was more than a mess, he hadn't replaced water in months and i had evaporated to the point where the filter couldnt intake anymore so it was turned off, its amazing there were any fish still alive, what I did when he gave me the fish was put them in a five gallon tank with an undergravel filter because I was moving out of the apartment for the summer, this was before I knew anything about cycling, but anyway, they survived and lived in that little tank for two months, and then I moved back into the old apartment, and then i cleaned out the entire ten gallon tank thouroughly because the water had evaporated even further and it was disgusting, then before i set it up, i decided I might as well learn about what I'm doing so i don't kill my fish, and thats when I learned about the cycling. so I bought a new filter (one that hangs over the top or the tank, and "aquaclear" for a 20 gallon tank), and then when i set up the tank and the filter, i took gravel from the 5 gallon tank and put it in a small layer right before the filter media in hopes that the bacteria from it would spread to the filter media, and the rest of the gravel i just laid across the top of the gravel on bottom of the tank. So im not sure if that means it's cycles or not, the tetras got fin rot right after I put them into the tank, but its almost fully healed now, so I don't know if it was the water or just the fact that they had their environment changed so drastically. Thanks for all your help, I wish I had learned all this stuff before. thanks