hi, i have a 15 gallon and i have quite alot of fish in there as you can tell by my signature, as long as you do weekly water changes you should be fine with quite alot, (maybe i do have to many!) but make sure your tank HAS cycled because my dad thinking he knows it all cycled his tank for 5 weeks without checking his water, then plomped in some livebearers and most of them are dead.