http://en.wikipedia.org/wiki/Oxymoron
Now that that's out of the way, there are a couple of things to consider:
1)
They grow really slow. As long as you're confident that you'll be able to upgrade, a 29G will suit a juvenile just fine for a decent amount of time.
2)
They do eventually get decently large. Having said that, you shouldn't need over 100G, as over 14" is rare in captivity. Think 75G for a single adult for life and you should be fine
most of the time.