lots of water changes they are a huge bio load, they eat anything and everything including tankmates.... you dont need a bigger tank you need a pond..... prepare to feed something in the neighborhood of an entire 2' fish every week in the future.
I have a RTC already. Hes young but getting huge!! quickly. I just bought that same fish today though. Its a RTC TSN crossbreed. Mine is tiny and i have him in a 45 gallon for now but you'll have to get a new tank sooner then later.. I learned this the hard way. My RTC grew 6 inches in 5 to 6 weeks.
You do realize that tank will last maybe a few months. Also, there is no max size yet as most hybrids on this forum have not stopped growing yet. Their max size has been estimated to be 6'
i have a rtc x tsn of my own and i have him in a 300 gallon rubbermaid, at 8 months he is in the neighborhood of 14-15 inches, and i was doing light feedings for 3 months trying to slow his growth because some problems had occured and i couldnt move him out of my 55. and he is still a brute after such light feeding, as soon as i started feeding more he took off in growth again. moral is you can slow them temporarily but there is nothing you can do to keep these fish from getting too massive for all but an enormous tank or a pond.