a rtc in a 65 that is that size should have atleast a 25% wc every other day. just because it eats and defecates soo much. keepers of large cats in ponds and massive tanks have to do wc's every feeding.
atleast a 150 gal tank? how about you add a 0 if youre talking for life. but as a grow out the 65 is a comfortable size so long as it isnt bumping into the sides all the time.