It could but I'd recommend just one clown fish. And no, they don't have to be in pairs - they don't get any lonelier than any other fish does and without mating/breeding behavior they're less territorial. Two paired clowns will basically have the entire tank as their territory in a 29 gallon. Also, make sure you get one of the smaller species of clown fish. With only one clown, you could probably also get a smaller personality fish - like a tail spot blenny or maybe a possum wrasse.