For no reason in particular, I visited our local Petsmart today, and was rewarded with a rare treat - in a tank of Otocinclus there were two dwarf corys - not pygmaeus, but I knew it must by one of the others. It turned out to be Corydoras habrosus, a Venezuelan species.
That pretty much decided the fate of the former Macropodus tank. I couldn't put the new corys into the main tank (they're a bit small to cohabitate with adult Macropodus), and I didn't want to add them to the plant tank without quarantining them first. So that left the former Macropodus tank. And since I didn't want to leave them as the sole occupants of the tank, I took the opportunity to buy a dozen Otocinclus, as Gary had recommended.