If you want three fish get a bigger tank. That tank isn't large enough for three fish, it just a fact. Looks like you need to alot more research but these small tanks are more for small coral gardens then lots of fish. You could set up a larger FO for about the same price as a nano-cube. I see that you are already underway with this project but having a big bioload will only cause problems (algae, death, etc...) and will discourage you. If you MUST have more fish look into a pair of false perc, banggai (sp?) cardinals, I'm not sure what else but keep in mind the adult size of the fish you put in there not just how big they are when you buy them.