I have a 5 gallon tank with about 12 younger plants in it, no filter or heater and a Leopard Danio in it right now. Want to keep it this way, with no heat or filter. Could a group of 3 danio work in this tank, or a pair? I don't have room for a larger tank, so need to make this one work. Would like to have at least two fish in there if possible. I would sure appreciate any ideas?