I keep several large cichlids... Jaguar, Red Texas, Green Terror, JD, Oscar, Salvini, Gold Severum and a Tinfoil Barb in a 475gal. If your 6 footer is a 180gal, you could combine any of these say 3 or 4. Beware male Jaguars, potential for 16+ ins and quite aggressive. Mine is female and at 4 yrs old and about 12ins, surely full grown. All these fish are very intelligent, colorful and full of personality. And very easy to feed/care for. Just my personal preferences, I'm sure you will enjoy whatever you decide on!