I received a shipment today of six RB piranhas from Aqua Scape. One of them was on about his last leg, but bounced right back when I put him in my aquarium. They are all six in my 20 gallon. Here's my question though..........I just got my new 55 gallon tank up & running tonight. I'll be away from home tomorrow though Saturday morning. How long can I safely let them all in that 20 gallon? I'm ordering Bio Spira which should arrive Monday for my new tank. I only plan to keep them until they are about 4 inches, then I'm gonna sell them to the local pet store & put two Dempseys in the 55 gallon. How dangerous of a biting hazard are these fish inso far as biting at one's hand while doing aquarium maintainence. At what size do they really become hazardous? I want to ship them out before then.