The 29 is my way of ensuring he eats as a small baby... the tank is filtered at about. 200g capacity. From his growth as of yet, he will last a decent time in the 75 before he gets moved again to the stock tub.
That makes sense if you are filtered at 200gal...you almost want a massive sump to keep the volume up but a small tank to keep him in one place but to be fair I think they search out food most of the time.