Go planted. I think that's best for small tanks. It really helps to keep the ammonia down in these nano tanks from my experience. I'm running a little 5.5G right no actually that has 2 bettas, but like stated above won't work with the fluval edge because of lack of room for O2. Go with plants and some tetras (rummy nose are my personal favorite) and maybe even a cory. I know some are gonna say that's overstocked but I've made it work for over a yr before with little problems with ammonia. Just don't rush the cycling part or you're gonna have crashes every week lol.