i have a 6 gallon tank, and i keep 3 plattys and a molly with 23 baby molleys that my one molly had like within an hour of getting home, so far, they all seem happy. i might upgrade to a 20 gallon tank sometime in the near future, maybe have 2, because i like the size and the tastefulness of my 6 gallon tank on my dresser. i dont think that you are limited very much by the 5 gallon tank, as long as you dont overcrowd it, and its better to get like 7 or 8 SMALL fish than 2 big fish.