is it ok to put in an 8 year old 8-9 inch piranha with 5, 5-6inch piranha's in a 100 gal tank? , if so what is the best way to introduce them, i was told to take all the existing piranha out of my tank, put them in a bucket [of the tank water of course] with the new piranha and then put them all back in the tank and that will kind of erase any original territorial instinct. is this true? thanks for your help