My sister has a 3 gal. round tank. The betta she had in it died yesterday(we're not sure why) so we did a 100% water change. Currently, the tank is sitting on the kitchen counter(it's new location) and we're letting it run for a couple days. Her question is "What can I put in it?" It has a UG filter, a heater, and an airstone. She wants to get another betta, but can we put another fish in with it? Maybe a platy, or a cherry barb to help it cycle? If we could fit two fish in there, should we add the first one and then, maybe a week later, the betta? Any suggestions are welcome! Thanks for your help!