He dosen't have to grow that fast. I'm not saying starve him, but you don't have to grow him right out of the tank. If you give him good water quality, superb filtration, frequent water changes, High quality food's, and a restricted diet. You will still have a very healthy rtc. And if you keep him by himself he will have a calmer disposition. So if you have the adequete filtration and care, than you can grow him larger in the tank than if he was with tankmates.