i had a single oscar in a 55 gal and never had problems with HITH. b/c he was "dirty" i did 50% water changes weekly. i will agree tho tht this is an absolute minimum tank size for them, but it can be done. everyone i think will agree tht given the funds they would love to put all their fish in a bigger tank but some of us arent fortunate enough to be able to have small ponds in our houses! you got a 65 with plenty enough turn around space. i'd say go 4 it if thts the fish you really want!