Yes, the weakest ones.Ah. By weak ones you mean the weaker piranhas in the group right.
Hm.. better to add straight to the 70 then eh
Also,I have seen some tanks with just a single piranha , is that okay or is it a must fer a shoal?
I don’t see a problem putting them right in the 70.
I kept my red solo, they feel more secure in groups but will do fine on their own. The Serrasalmus genus do best alone though. Shoal gives that feeding reaction that they are famous for though.