i wanted to get 6 rbp's in my 65 gallon tank. would i be over crowding them? i think i read in a post a while back it's better to have an odd number in the tank. is that true? also i have 2 jack dempsey's and 1 cory catfish in there. They are about quarter sized. how long til the piranha's eat them? i wanted to pick up dime sized piranha's. I don't really care if they jack dempsey's get eaten cuz are just there to help with the cycling.