YES finally. Someone besides me thinks 55 gallons is way too small for a shoal of red bellies. 1 RBP will do OK in a 55.
You shouldn't all be shocked when a piranha or 2 dies in your 55 gallon, because that tank is way to small for more then 1.
Like Diogenes said, the sanchezi, or a manny for a while would be a perfect solo piranha for the 55.