I had a single specimen maybe 5 years ago in a 125gal, very active piranha when they are solitary, sort of active like the Elongatus. Had a great appetite and are very hardy. Personally the smallest tank I would put them in is a 75gal, but that's for a single fish. for multiple for a shoal I would do a 180gal, because they are vicious fin nippers and your specimen wont look as good as far as fins lol.