Most people say at least 2.5 gallons. While you *could* keep a betta in a 1 gallon it is much better for them to live in a bigger tank. They are happier, and have more room to swim. Plus, less water changes for you.
I picked up one of those tanks as an emergency tank (for bettas) and it is kind of small. It's a good tank but the way the lid is constructed you can't use a heater. (At least the heaters I like.) There are two holes for feeding on either side of the lid and the plug doesn't fit through. The only indent in the hood is there to allow the filter chord to leave the tank. They are super easy to clean though. (depending on what you use on the bottom of your tank.) The light in it is a 7 watt chandelier bulb and the light shield screws onto the hood, so it is difficult to change the bulb. Both the Aqueon 1 and the Aqueon 2.5 have the same filters, and a Fluval Edge pre-filter sponge fits nicely on the intake tubes so the Bettas don't get sucked in.
If you want a small 2.5 tank for a Betta the Aqueon 2.5 is a nice tank, it is also really easy to clean and runs the same filter. The hood in the 2.5 takes standard incandescent bulbs for aquarium hoods. They run about $30 - $40.
I looked up the blood parrots, and the wiki on them says they can grow up to 8 inches! The minimum size tank for one is probably going to be 15+ gallons.
I would go to the chichlid forum of tropicalfishkeeping.com (this forum) and find out what you can.
I would really get the poor chichlid out of the 1 gallon ASAP.