I've found C. pygmaeus to be much hardier than C. habrosus. I've got a school of C. pygmaeus in a 33 gallon tank in my wife's classroom where they get fed 5 out of 7 days and get monthly water changes at best. On the other hand, I have a 15 in my house that gets a 20% weekly water change religiously, and I cannot keep C. habrosus alive for more than a week in it. They have got to have well aged water, evidently.
While I agree that sand is an indispensible substrate for any cory tank, it's also useful to set aside an area for marbles or large, smooth pebbles. While adult cories do best in sand, a pebble bed will allow some fry to survive noshing on the infusoria growing on the trapped food particles out of siht and reach of their tankmates. If the cories should spawn, that is.