they get 9in. tops all day they LOVE live blackworms and frozen bloodworms they are very nocturnal I'd say a 55g. would do them just fine, I've always kept them solo as far as other elephant trunks go but I've seen them in groups I was always told keep electric fish by singlely with one BGK one elephant nose etc...... their cool with tetras, barbs, NON aggresssive cichlids like geo's, angelfish, bichirs......