If you are talking a 6' tank id go with 180. Gives you 24" front to back and 24" top to bottom. A long time ago I had Africans. I mixed the as any fledgling fish keeper does but built a nice slate stack for them and it looked great. All the smaller 4-6 inchers looked right at home and I had breeding pairs all the time. I had one frontosa in there it grew to adult size the 125 looked small and the fish looked cramped.180 with the extra depth would have been better. The extra top to bottom of a 220 wouldn't be needed but wouldn't hurt either, but its a pia to clean.
