Calvus do well with most other Tanganyikans. If they are 3 or 4 inches then they are proably about 5 years old or so. Calvus are extreamly slow growers. I keep mine with N. Buscheri, N. Bachardi, N. Lepeupi, N. Tret and Julidochromis with very few problems. As for a 29 gal a Pair would do just...