yeah rtc needs a very big tank. when theyre still small not much problem coz rtc will stay mainly on the bottom but when they get bigger, they become ultra ravenous! a cousin of mine kept one and it ate everything in his tank
I had a rtc and a arro in the same tank for about 6 mos. The arro was alot bigger than the rtc when I got them both, but within that time period the arro knew he would be food if I didn't keep them feed. You could see it in his eyes !