My dad moved his two rb piranhas into a 55g tank about two months ago and now ones dead. I got them for him last fathers day and all was good. Is it because the weren't in a scoll? I told him to add two more but he liked having just two. Now the one ate the other. Anyway i was wondering can i buy 3 new ones at a smaller size and add them? The one he has is about 6inches. I don't know much on them but i think if i add just one it would get killed right away because now the one owns the whole tank. any info would be great thank you.