I keep mine with Serpae, Diamond, Columbian, and Lemon Tetras. Even though my Flagtail is quite large (8") it doesn't bother the little Tetras at all.
Do be aware that Prochilodus get quite large and are very active - a 180G would probably be the minimum long term tank for one. My 210 is starting to seem almost too small...
yeah thats the down side. i have a 125 and i think itll be too small im just looking for a cool oddball fish that wont eat my fish lol. i might end up getting silver dollars.