set it up and let it run for a week (don't forget the dechlorinator!) then get some feeders guppies rosie reds or goldfish whatever your new monster will eat
think of it as a "first supper"
btw check out some of the syndontis catfish some of them would be happy in a 29 also check out batrochoglannis raninus (bumblebee catfish or dwarf marbled catfish) they only get to be about 6" but they will eat anything it can even partly stuff into it's mouth it may not be big but it's a monster in my bookalso check out half beaks