Given the overstocked and active tank you have, it's very unlikely they'll ever feel comfortable enough to breed. I'd suggest moving them out to their own tank (at least a 10, a little bigger if possible). Bump the temperature up a bit (low 80's) and drop the water level a bit. You'll also need something at the surface for the male to build his bubble nest on, floating plants are ideal. Avoid strong currents that would disrupt the nest.
Are you sure you have a mated pair?