I have just seen a tank with at least 60 / 80 malawi's if not possibly more in a 5ft x 2ft x 20 being filtered by a Eheim 2222 is this a good thing won't they fight?
Overcrowding reduces aggression because there are more fish for the most aggressive ones to disperse it upon. When it comes to mbuna the only limitations on stocking levels are the aquarists capabilities of upkeeping the tank. A 5x2 tank is pretty big too.
Eheim2228 with efi substrate and ceramic rings would be ideal and have the other eheim set up with sponges and filter floss.This will polish up the water as you have a highish stock level