Recommended? I wouldn't recommend anything smaller than a 3' tank with some depth to it. A 29 is usually suitable, with care in choosing tankmates. Some people keep breeding pairs in 20H's, though I think that's a bit on the small side.
"What, exactly, is the internet? Basically it is a global network exchanging digitized data in such a way that any computer, anywhere, that is equipped with a device called a 'modem', can make a noise like a duck choking on a kazoo." - Dave Barry